[media] V4L: videobuf, don't use dma addr as physical

mem->dma_handle is a dma address obtained by dma_alloc_coherent which
needn't be a physical address in presence of IOMMU, as
a hardware IOMMU can (and most likely) will return a bus address where
physical != bus address.

So ensure we are remapping (remap_pfn_range) the right page in
__videobuf_mmap_mapper by using virt_to_phys(mem->vaddr) and not
mem->dma_handle.

While at it, use PFN_DOWN instead of explicit shift.

[mchehab@redhat.com: Fix compilation breakage due to the lack of a comma]
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>