msm: vidc: Don't assume session error as sys error

Currently driver assumes all session errors as
sys error. Sys error releases video core which
is not required in case of session errors.
So treat session error as session error only
instead of sys error.

CRs-Fixed: 2138904
Change-Id: I848aad12b07ac547a7073fecbc9b264b5c9b1289
Signed-off-by: Maheshwar Ajja <majja@codeaurora.org>