usb: gadget: configfs: include appropriate header file in configfs.c
usb: gadget: configfs: include appropriate header file in configfs.c

Include appropriate header file drivers/usb/gadget/configfs.h in
gadget/configfs.c because function unregister_gadget_item() has its
prototype declaration in gadget/configfs.h.

This eliminates the following warning in gadget/configfs.c:
drivers/usb/gadget/configfs.c:994:6: warning: no previous prototype for ‘unregister_gadget_item’ [-Wmissing-prototypes]

Signed-off-by: Rashika Kheria <62a2cbd3422b0d621dafb7ceeff40187aeaed4ed@gmail.com>
Reviewed-by: Josh Triplett <c028c213ed5efcf30c3f4fc7361dbde0c893c5b7@joshtriplett.org>
Signed-off-by: Felipe Balbi <94dddeeef08b001e003cce128ddc162a4e2c6cd2@ti.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs