net: phy: mediatek: Improve readability of mtk-phy-lib.c's mtk_phy_led_hw_ctrl_set()

This patch removes parens around TRIGGER_NETDEV_RX/TRIGGER_NETDEV_TX in
mtk_phy_led_hw_ctrl_set(), which improves readability.

Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: SkyLake.Huang <skylake.huang@mediatek.com>
Signed-off-by: David S. Miller <davem@davemloft.net>