media: coda/imx-vdoa: Check for platform_get_resource() error

platform_get_resource() may fail and in this case a NULL dereference
will occur.

Prevent this from happening by returning an error on
platform_get_resource() failure.

Fixes: b0444f18

 ("[media] coda: add i.MX6 VDOA driver")

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>