dt-bindings: net: Fix a typo in the phy-mode list for ethernet bindings

The phy_mode "2000base-x" is actually supposed to be "1000base-x", even
though the commit title of the original patch says otherwise.

Fixes: 55601a88 ("net: phy: Add 2000base-x, 2500base-x and rxaui modes")
Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>