V4L/DVB: videobuf: Rename vmalloc fields to vaddr

The videobuf_dmabuf and videobuf_vmalloc_memory fields have a vmalloc
field to store the kernel virtual address of vmalloc'ed buffers. Rename
the field to vaddr.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>