[][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
1 file changed