msm: msm_dsps: Disable the DSPS watchdog before shutdown

The DSPS watchdog timer continues counting even after
the DSPS is shutdown. This may cause a spurious watchdog
interrupt after the DSPS is powered up, before the software
running on the processor can re-init the watchdog. Disable
the watchdog before shutting down the watchdog.

Change-Id: I169e690b82ae05617e096ac832d757a110f673a4
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>