msm: camera: ope: handle unlocking in process timer

In process timer, if there are no empty taks then it
returns without unlocking context mutext. This lead
to deadlock later if other tasks are waiting on this
lock.

CRs-Fixed: 2823721
Change-Id: I478d1797be59d975e9d58e005a5fad5c22656f51
Signed-off-by: Alok Chauhan <alokc@codeaurora.org>