mediatek: fix 2.5G PHY LED polarity for MT7987

mediatek: fix 2.5G PHY LED polarity for MT7987

The patch that adds MT7987 support to the mtk-2p5ge
driver does the following:

case MTK_2P5GPHY_ID_MT7987:
	phy_clear_bits_mmd MTK_PHY_LED_ON_POLARITY
case MTK_2P5GPHY_ID_MT7988:
	phy_set_bits_mmd.. MTK_PHY_LED_ON_POLARITY

phy_set_bits_mmd... MTK_PHY_LED_ON_POLARITY | xxx

This clearly resulted in the LED polarity of the 2.5G PHY
on the MT7987 being reversed. Remove redundant MMD operations
to fix the 2.5G PHY LED error on Bananapi BPi-R4 Lite.

Fixes: d62fc50f ("mediatek: import patches from SDK to support MT7987 Ethernet")
Signed-off-by: Chukun Pan <amadeus@jmu.edu.cn>