[media] Drivers: staging: media: davinci_vpfe: Use resource_size function

Use resource_size function on resource object instead of explicit
computation.

Signed-off-by: Alexandru Gheorghiu <gheorghiuandru@gmail.com>
Acked-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>