wifi: mwifiex: mark a variable unused

We need to read a value from the device to wake it, but if it
succeeds we don't really care about it. Mark the variable to
avoid a compiler warning.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220904212910.5d67f55178a1.If0789ab326935896e5886fa06dbb9ef0da6c0b41@changeid

drivers/net/wireless/marvell/mwifiex/pcie.c

@@ -644,7 +644,7 @@ static int mwifiex_pm_wakeup_card(struct mwifiex_adapter *adapter)
 {
 	struct pcie_service_card *card = adapter->card;
 	const struct mwifiex_pcie_card_reg *reg = card->pcie.reg;
-	int retval;
+	int retval __maybe_unused;
 
 	mwifiex_dbg(adapter, EVENT,
 		    "event: Wakeup device...\n");