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: f27abde3 ("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>