[media] zc3xx: remove dead code and uneeded gotos

As reported by smatch:
	drivers/media/usb/gspca/zc3xx.c:5994 transfer_update() info: ignoring unreachable code.

That happens because there's a return that it is never called,
as the work queue runs an infinite loop, except when the device is
put to sleep or an error happens.

When an error happens, a break statement is enough to go out of
the loop. So, let's remove the goto, as break is the typical
instruction used to end a loop.

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>