Documentation/bindings: phy: update references to cp11x

The cp11x references in dts has changed, reflect it in comphy
documentation.

Signed-off-by: Grzegorz Jaszczyk <jaz@semihalf.com>
Signed-off-by: Konstantin Porotchkin <kostap@marvell.com>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>