[media] videobuf2-core: fix a warning at vb2

It seems that a cut-and-past error were added by the last patch:

drivers/media/video/videobuf2-core.c: In function ‘vb2_qbuf’:
drivers/media/video/videobuf2-core.c:1099:14: warning: comparison between ‘enum v4l2_buf_type’ and ‘enum v4l2_memory’ [-Wenum-compare]

On all places V4L2_MEMORY_USERPTR is used, it is associated with
q->memory, and not b->type. So, the fix seems obvious.

Cc: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Pawel Osciak <pawel@osciak.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>