cnss2: Add code to address boot timer debug corner case

To handle corner case where mhi power on success and the boot
debug timer handler execution(i.e dumping register) runs parellel.
Even-though the timer is deleted as soon as mhi is powered on,
as this handler is still running it is armed again. Use
del_timer_sync which makes sure the timer is not queued and
the handler is not running upon its exit.

Change-Id: Ie428f3e8af8870018dfed99a5472afca14116bb3
Signed-off-by: Mohammed Siddiq <quic_msiddiq@quicinc.com>