phy: marvell: Rename mii_lpa_to_linkmode_lpa_t

Rename mii_lpa_to_linkmode_lpa_t to mii_lpa_mod_linkmode_lpa_t to
indicate it modifies the passed linkmode bitmap, without clearing any
other bits.

Also, ensure bit are clear which the lpa indicates should not be set.

Fixes: c0ec3c27

 ("net: phy: Convert u32 phydev->lp_advertising to linkmode")
Suggested-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>