wifi: mt76: mt7921: Fix use-after-free in fw features query.

Stop referencing 'features' memory after release_firmware is called.

Fixes this crash:

RIP: 0010:mt7921_check_offload_capability+0x17d
mt7921_pci_probe+0xca/0x4b0
...
Signed-off-by: Ben Greear <greearb@candelatech.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Acked-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/51fd8f76494348aa9ecbf0abc471ebe47a983dfd.1679502607.git.lorenzo@kernel.org

drivers/net/wireless/mediatek/mt76/mt7921/init.c

@@ -171,12 +171,12 @@ mt7921_mac_init_band(struct mt7921_dev *dev, u8 band)
 
 u8 mt7921_check_offload_capability(struct device *dev, const char *fw_wm)
 {
-	struct mt7921_fw_features *features = NULL;
 	const struct mt76_connac2_fw_trailer *hdr;
 	struct mt7921_realease_info *rel_info;
 	const struct firmware *fw;
 	int ret, i, offset = 0;
 	const u8 *data, *end;
+	u8 offload_caps = 0;
 
 	ret = request_firmware(&fw, fw_wm, dev);
 	if (ret)
@@ -208,7 +208,10 @@ u8 mt7921_check_offload_capability(struct device *dev, const char *fw_wm)
 		data += sizeof(*rel_info);
 
 		if (rel_info->tag == MT7921_FW_TAG_FEATURE) {
+			struct mt7921_fw_features *features;
+
 			features = (struct mt7921_fw_features *)data;
+			offload_caps = features->data;
 			break;
 		}
 
@@ -218,7 +221,7 @@ u8 mt7921_check_offload_capability(struct device *dev, const char *fw_wm)
 out:
 	release_firmware(fw);
 
-	return features ? features->data : 0;
+	return offload_caps;
 }
 EXPORT_SYMBOL_GPL(mt7921_check_offload_capability);