iwlwifi: iwl-dbg: Use del_timer_sync() before freeing

iwlwifi: iwl-dbg: Use del_timer_sync() before freeing

In Chrome OS, a large number of crashes is observed due to corrupted timer
lists. Steven Rostedt pointed out that this usually happens when a timer
is freed while still active, and that the problem is often triggered
by code calling del_timer() instead of del_timer_sync() just before
freeing.

Steven also identified the iwlwifi driver as one of the possible culprits
since it does exactly that.

Reported-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Johannes Berg <johannes.berg@intel.com>
Cc: Gregory Greenman <gregory.greenman@intel.com>
Fixes: 60e8abd9d3e91 ("iwlwifi: dbg_ini: add periodic trigger new API support")
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Gregory Greenman <gregory.greenman@intel.com>
Tested-by: Sedat Dilek <sedat.dilek@gmail.com> # Linux v5.17.3-rc1 and Debian LLVM-14
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220411154210.1870008-1-linux@roeck-us.net