msm: vidc: Increase firmware unload delay

Using the same delay for power collapse and
firmware unload can trigger race conditions in
the power collapse and firmware unload sequences.
Increase the firmware unload delay from 10 seconds
to 15 seconds to avoid this.

Change-Id: I0fbde99e8c7fca93f7b227d351a73c580e244614
Signed-off-by: Maheshwar Ajja <majja@codeaurora.org>