net: phy: mscc: the extended page access register is 16 bits

The Extended Page Access is a 16-bit register, so change the page
parameter of vsc85xx_phy_page_set to a u16.

Signed-off-by: Quentin Schulz <quentin.schulz@bootlin.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>