brcmfmac: only lock and unlock fws if fws is not null

There is a null ptr check for fws to set bcmc_credit_check, however,
there a lock and unlock on fws should only performed if fwts is
also not null to also avoid a potential null pointer deference.
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Acked-by: NArend van Spriel <arend@broadcom.com>
Signed-off-by: NKalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/broadcom/brcm80211/brcmfmac/fwsignal.c

@@ -1609,10 +1609,11 @@ static int brcmf_fws_notify_bcmc_credit_support(struct brcmf_if *ifp,
 {
 	struct brcmf_fws_info *fws = ifp->drvr->fws;
 
+	if (fws) {
 		brcmf_fws_lock(fws);
-	if (fws)
 		fws->bcmc_credit_check = true;
 		brcmf_fws_unlock(fws);
+	}
 	return 0;
 }