usb: gadget: Assign boolean values to a bool variable

Fix the following coccicheck warnings:

./drivers/usb/gadget/udc/udc-xilinx.c:846:1-17: WARNING: Assignment of
0/1 to bool variable.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Link: https://lore.kernel.org/r/1612678696-15794-1-git-send-email-jiapeng.chong@linux.alibaba.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>