msm: vidc: Do not halt axi after subsystem_put

Avoid any Venus register read or write after subsystem_put.
Without this patch we occasionally see AHB timeout and device
crash while trying to read the halt axi register after unloading
the firmware.

Change-Id: I5105e3f6bd37d6c12d256a35c9558c1ac6f4028c
Signed-off-by: Arun Menon <avmenon@codeaurora.org>