V4L/DVB (8209): uvcvideo: Don't free URB buffers on suspend.

All submitted URBs must be killed at suspend time, but URB buffers don't have
to be freed. Avoiding a free on suspend/reallocate on resume lowers the presure
on system memory.

Signed-off-by: Laurent Pinchart <laurent.pinchart@skynet.be>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>