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 <[e-mail]>
Cc: Steven Rostedt <[e-mail]>
Cc: Johannes Berg <[e-mail]>
Cc: Gregory Greenman <[e-mail]>
Fixes: 60e8abd9d3e91 ("iwlwifi: dbg_ini: add periodic trigger new API support")
Signed-off-by: Guenter Roeck <[e-mail]>
Acked-by: Gregory Greenman <[e-mail]>
Tested-by: Sedat Dilek <[e-mail]> # Linux v5.17.3-rc1 and Debian LLVM-14
Signed-off-by: Kalle Valo <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/net/wireless/intel/iwlwifi/iwl-dbg-tlv.c

···
 	struct iwl_dbg_tlv_timer_node *node, *tmp;
 
 	list_for_each_entry_safe(node, tmp, timer_list, list) {
-		del_timer(&node->timer);
+		del_timer_sync(&node->timer);
 		list_del(&node->list);
 		kfree(node);
 	}