msm: vidc: Return only active state VBs during flush

When video core is in invalid state and client have requested
for flush, driver iterates over the queued list and returns
buffer to videobuf. It may happen that some buffer in queued
list were not in active state. Driver is not suppose to send
back those buffers to videobuf. Adding the state check to
ensure the same.

CRs-Fixed: 2052760
Change-Id: If7bec10c465dc8066dbbf6fcfff9f407c41e36ce
Signed-off-by: Vikash Garodia <vgarodia@codeaurora.org>