qcacmn: Flush reg work instead of cancelling in deinit path

Currently reg work is being cancelled in deinit path,
cancel work will remove all the pending work items
and wait for completion of current executing work.
But in reg work case even pending work items has to be
executed because we don't want to skip HP/TP values update.

To avoid this make sure all the pending reg work items are
flushed then disable the work for further queueing.

Change-Id: I2ba1e26cf41fb3b0c33ec584c56525cbfac94d8f
CRs-Fixed: 3065038