[][kernel][common][eth][Remove unnecessary PHY power down operation]

[Description]
Remove unnecessary PHY power down operation.

If without this patch, the internal GPHY might power doen when disabling
the external GPHY.

[Release-log]
N/A


Change-Id: I72bd975e82ffaa03251a5a953b2a8c07073fed6e
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/7256585
1 file changed