Fixes the following W=1 kernel build warning(s):

 drivers/usb/cdns3/cdns3-gadget.c:163: warning: expecting prototype for select_ep(). Prototype was for cdns3_select_ep() instead
 drivers/usb/cdns3/cdns3-gadget.c:2025: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 drivers/usb/cdns3/cdns3-gadget.c:2224: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 drivers/usb/cdns3/cdns3-gadget.c:2247: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 drivers/usb/cdns3/cdns3-gadget.c:2264: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 drivers/usb/cdns3/cdns3-gadget.c:2399: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 drivers/usb/cdns3/cdns3-gadget.c:2489: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 drivers/usb/cdns3/cdns3-gadget.c:2589: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 drivers/usb/cdns3/cdns3-gadget.c:2656: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 drivers/usb/cdns3/cdns3-gadget.c:2677: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 drivers/usb/cdns3/cdns3-gadget.c:2722: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 drivers/usb/cdns3/cdns3-gadget.c:2768: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 drivers/usb/cdns3/cdns3-gadget.c:2877: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 drivers/usb/cdns3/cdns3-gadget.c:2923: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
 drivers/usb/cdns3/cdns3-gadget.c:2986: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst

Cc: Peter Chen <peter.chen@kernel.org>
Cc: Pawel Laszczak <pawell@cadence.com>
Cc: Roger Quadros <rogerq@kernel.org>
Cc: Aswath Govindraju <a-govindraju@ti.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Pawel Jez <pjez@cadence.com>
Cc: linux-usb@vger.kernel.org
Acked-by: NPeter Chen <peter.chen@kernel.org>
Signed-off-by: NLee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20210526130037.856068-8-lee.jones@linaro.orgSigned-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>