V4L/DVB: v4l videobuf: rename .vmalloc to .vaddr

Rename the .vmalloc op in struct videobuf_qtype_ops to .vaddr. This op returns
the virtual kernel address of a buffer. vaddr is a lot less confusing than
vmalloc since this callback does do any allocations.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>