usb/gadget: (fusb300_udc) Remove unused function fusb300_ep0_complete

fusb300_ep0_complete() is an empty function, not called from anywhere,
and causes the following build warning.

fusb300_udc.c:983: warning: fusb300_ep0_complete defined but not used

Remove it.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>