The pwc driver causes a warning when CONFIG_USB_PWC_INPUT_EVDEV is unset:
drivers/media/usb/pwc/pwc-if.c: In function 'usb_pwc_probe':
drivers/media/usb/pwc/pwc-if.c:1115:1: warning: label 'err_video_unreg' defined but not used [-Wunused-label]
This moves the unused label and code inside another #ifdef to
get rid of the warning.