usb: gadget: s3c: remove unused 'udc' variable

Remove unused 'udc' variable to fix compile warnings:

    drivers/usb/gadget/udc/s3c2410_udc.c: In function 's3c2410_udc_dequeue':
    drivers/usb/gadget/udc/s3c2410_udc.c:1268:22: warning: variable 'udc' set but not used [-Wunused-but-set-variable]

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Link: https://lore.kernel.org/r/20200731074122.6484-1-krzk@kernel.org