usb: gadget.h: be consistent at kernel doc macros

There's one value that use spaces instead of tabs to ident.
That causes the following warning:

./include/linux/usb/gadget.h:193: ERROR: Unexpected indentation.
Signed-off-by: NMauro Carvalho Chehab <mchehab@s-opensource.com>
Acked-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

include/linux/usb/gadget.h

@@ -188,7 +188,7 @@ struct usb_ep_caps {
  * @caps:The structure describing types and directions supported by endoint.
  * @maxpacket:The maximum packet size used on this endpoint.  The initial
  *	value can sometimes be reduced (hardware allowing), according to
- *      the endpoint descriptor used to configure the endpoint.
+ *	the endpoint descriptor used to configure the endpoint.
  * @maxpacket_limit:The maximum packet size value which can be handled by this
  *	endpoint. It's set once by UDC driver when endpoint is initialized, and
  *	should not be changed. Should not be confused with maxpacket.