net: pcs: xpcs: actively unset DW_VR_MII_DIG_CTRL1_2G5_EN for 1G SGMII

xpcs_config_2500basex() sets DW_VR_MII_DIG_CTRL1_2G5_EN, but
xpcs_config_aneg_c37_sgmii() never unsets it. So, on a protocol change
from 2500base-x to sgmii, the DW_VR_MII_DIG_CTRL1_2G5_EN bit will remain
set.

Fixes: f27abde ("net: pcs: add 2500BASEX support for Intel mGbE controller")
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/20250114164721.2879380-2-vladimir.oltean@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: vladimiroltean

drivers/net/pcs/pcs-xpcs.c

@@ -685,7 +685,8 @@ static int xpcs_config_aneg_c37_sgmii(struct dw_xpcs *xpcs,
 		return ret;
 
 	val = 0;
-	mask = DW_VR_MII_DIG_CTRL1_MAC_AUTO_SW;
+	mask = DW_VR_MII_DIG_CTRL1_2G5_EN | DW_VR_MII_DIG_CTRL1_MAC_AUTO_SW;
+
 	if (neg_mode == PHYLINK_PCS_NEG_INBAND_ENABLED)
 		val = DW_VR_MII_DIG_CTRL1_MAC_AUTO_SW;