msm: vidc: Remove unnecessary get/put_inst()

Without checking the get_inst() return type is leading to
wrongly destroying instance in put_inst() if return type
is NULL. get_inst() return type will be NULL if inst->session
was removed. No need to have get_inst() and put_inst() in
forward path because the instance will be present in
forward path always.

CRs-Fixed: 2177935
Change-Id: I8055a16652a65fdf83f48ab5b186b52ff1479e7f
Signed-off-by: Maheshwar Ajja <majja@codeaurora.org>
Signed-off-by: Salman Syed <ssalman@codeaurora.org>