[][kernel][common][eth][Fix Coverity scan warning]

[Description]
Fix Coverity scan warning.
    - Fix missing unlock in the mtk_usxgmii_pcs_config().

[Release-log]
N/A


Change-Id: Ic72f682c0f3ee7133b085938bbb9019d0829c666
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/8435435
diff --git a/target/linux/mediatek/files-5.4/drivers/net/ethernet/mediatek/mtk_usxgmii.c b/target/linux/mediatek/files-5.4/drivers/net/ethernet/mediatek/mtk_usxgmii.c
index cdb2a55..f114225 100644
--- a/target/linux/mediatek/files-5.4/drivers/net/ethernet/mediatek/mtk_usxgmii.c
+++ b/target/linux/mediatek/files-5.4/drivers/net/ethernet/mediatek/mtk_usxgmii.c
@@ -594,8 +594,10 @@
 		xfi_mode = FIELD_PREP(USXGMII_XFI_RX_MODE, USXGMII_XFI_RX_MODE_5G) |
 			   FIELD_PREP(USXGMII_XFI_TX_MODE, USXGMII_XFI_TX_MODE_5G);
 		adapt_mode = USXGMII_RATE_UPDATE_MODE;
-	} else
+	} else {
+		spin_unlock(&mpcs->regmap_lock);
 		return -EINVAL;
+	}
 
 	adapt_mode |= FIELD_PREP(USXGMII_RATE_ADAPT_MODE, USXGMII_RATE_ADAPT_MODE_X1);