ath10k: cancel the event work in wlan snoc driver module remove

The ath10k snoc driver has two work handlers for the qmi event
processing and serializations of event processing. These two
event work handler must be sync and canceled in driver remove
method to avoid module unload and load failure due to the active
event work handler during device object memory free.

Change-Id: I546c6ba5404e6a26b22b5ef6155e092e279f2c71
Signed-off-by: Sarada Prasanna Garnayak <sgarna@codeaurora.org>