V4L/DVB (8256): uvc/uvc_v4l2.c: suppress uninitialized var warning

drivers/media/video/uvc/uvc_v4l2.c: In function `uvc_v4l2_mmap':
drivers/media/video/uvc/uvc_v4l2.c:1035: warning: 'buffer' might be used uninitialized in this function

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