qtnfmac: check band before allocating cmd_skb to avoid resource leak

The current code allocates cmd_skb and then will leak this if band->band
is an illegal value. It is simpler to sanity check the band first before
allocating cmd_skb so that we don't have to free cmd_skb if an invalid
band occurs.

Detected by CoverityScan, CID#1437561 ("Resource Leak")
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Reviewed-by: NIgor Mitsyanko <igor.mitsyanko.os@quantenna.com>
Signed-off-by: NKalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/quantenna/qtnfmac/commands.c

@@ -1300,12 +1300,6 @@ int qtnf_cmd_get_mac_chan_info(struct qtnf_wmac *mac,
 	int ret = 0;
 	u8 qband;
 
-	cmd_skb = qtnf_cmd_alloc_new_cmdskb(mac->macid, 0,
-					    QLINK_CMD_CHANS_INFO_GET,
-					    sizeof(*cmd));
-	if (!cmd_skb)
-		return -ENOMEM;
-
 	switch (band->band) {
 	case NL80211_BAND_2GHZ:
 		qband = QLINK_BAND_2GHZ;
@@ -1320,6 +1314,12 @@ int qtnf_cmd_get_mac_chan_info(struct qtnf_wmac *mac,
 		return -EINVAL;
 	}
 
+	cmd_skb = qtnf_cmd_alloc_new_cmdskb(mac->macid, 0,
+					    QLINK_CMD_CHANS_INFO_GET,
+					    sizeof(*cmd));
+	if (!cmd_skb)
+		return -ENOMEM;
+
 	cmd = (struct qlink_cmd_chans_info_get *)cmd_skb->data;
 	cmd->band = qband;
 	ret = qtnf_cmd_send_with_reply(mac->bus, cmd_skb, &resp_skb, &res_code,