V4L/DVB (13598): videobuf_dma_contig_user_get() for non-aligned offsets

If a USERPTR address that is not aligned to page boundary is passed to the
videobuf_dma_contig_user_get() function, it saves a page aligned address to
the dma_handle. This is not correct. This issue is observed when using USERPTR
IO machism for buffer exchange.

Updates from last version:-

Adding offset for size calculation as per comment from Magnus Damm. This
ensures the last page is also included for checking if memory is
contiguous.

Signed-off-by: Muralidharan Karicheri <m-karicheri2@ti.com>
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>