msm: modem-8660: Ignore unnecessary SMSM_RESET notifications

Before the modem is shutdown, the SMSM_RESET bit is set to
notify the modem to allow it to flush caches and complete
its error handler operations. One of these operations is
to set its own SMSM_RESET bit and notify the apps. This
notification is forwarded by modem_notifier to the
modem_8660 driver. Since the modem is already being
shutdown, this notification needs to be ignored.

Previously modem-8660 would unregister for the notification
and re-register for it once the modem was shutdown. This
may result in a race where the notification is sent after
the re-registration, a condition more exposed on 3.0 kernels.

Change the mechanism to use a flag to ignore the SMSM_RESET
notification inside the notification handler.

Change-Id: Ia49e76950afd04d8dfde1ca66e44d4231a366b31
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>