Documentation: DocBook: elieminate doc build break

Gadget function files have been moved to a "function" subdirectory.
Signed-off-by: NAndrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: NFelipe Balbi <balbi@ti.com>

Documentation/DocBook/gadget.tmpl

@@ -556,11 +556,11 @@ been converted to this framework.
 Near-term plans include converting all of them, except for "gadgetfs".
 </para>
 
-!Edrivers/usb/gadget/f_acm.c
-!Edrivers/usb/gadget/f_ecm.c
-!Edrivers/usb/gadget/f_subset.c
-!Edrivers/usb/gadget/f_obex.c
-!Edrivers/usb/gadget/f_serial.c
+!Edrivers/usb/gadget/function/f_acm.c
+!Edrivers/usb/gadget/function/f_ecm.c
+!Edrivers/usb/gadget/function/f_subset.c
+!Edrivers/usb/gadget/function/f_obex.c
+!Edrivers/usb/gadget/function/f_serial.c
 
 </sect1>