qcacmn: Release the platform_info spin lock before del_timer_sync

In qdf_mc_timer_stop_sync acquires the platform_info spinlock
and call's the del_tymer_sync. del_timer_sync waits for callbacks
to execute all CPU's. But callback scheduler_mc_timer_callback
tries to acquire the platform_info lock to execute. This can
lead to deadlock.

Change-Id: Ib21ee5b57e11d1c98e1308ee5318fb47d78a6ba2
CRs-Fixed: 2453603