st/va: add more errors checks in vlVaBufferSetNumElements and vlVaMapBuffer
Signed-off-by:Julien Isorce <j.isorce@samsung.com> Reviewed-by:
Christian König <christian.koenig@amd.com> (cherry picked from commit 5e763aaa) Nominated-by:
Emil Velikov <emil.velikov@collabora.co.uk>