iwlwifi: dbg: mark a variable __maybe_unused

If CONFIG_IWLWIFI_DEBUGFS is not set, the variable is assigned
but not checked, resulting in a compiler warning. Suppress it,
we need the variable for the debugfs-enabled case.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20200425130140.485f886f5a6c.I8a91c560c26cced33b15d8419caebb53a9abcc2d@changeid

drivers/net/wireless/intel/iwlwifi/fw/dbg.c

@@ -2760,7 +2760,7 @@ void iwl_fw_dbg_stop_restart_recording(struct iwl_fw_runtime *fwrt,
 				       struct iwl_fw_dbg_params *params,
 				       bool stop)
 {
-	int ret = 0;
+	int ret __maybe_unused = 0;
 
 	if (test_bit(STATUS_FW_ERROR, &fwrt->trans->status))
 		return;