msm: vidc: Fail qbuf and prepare_buf incase of error

If either instance state or core state is invalid, then
we should fail and return error from qbuf and prepare_buf.

CRs-Fixed: 973430

Change-Id: I925161cf70726f1f3d4d2abd5b1c84db204d7996
Signed-off-by: Arun Menon <avmenon@codeaurora.org>