The videobuf2-dma-contig allocator returns an ERR_PTR() on failure, not
a NULL like all other allocators. Fix videobuf2-core to also correctly
recognise those failures.
Signed-off-by: NGuennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>