net: stmmac: mdio: clean up c22/c45 accessor split

The C45 accessors were setting the GR (register number) field twice,
once with the 16-bit register address truncated to five bits, and
then overwritten with the C45 devad. This is harmless since the field
was being cleared prior to being updated with the C45 devad, except
for the extra work.

Remove the redundant code.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/E1urGBn-00000000DCH-3swS@rmk-PC.armlinux.org.uk


Signed-off-by: Jakub Kicinski <kuba@kernel.org>