net: phy: marvell: optimize logic for page changing during init

Instead of remembering if the page was changed, just compare the current
page to the saved one. This is easier and has the advantage to save a
register write if the page was already restored.

Signed-off-by: Uwe Kleine-König <uwe@kleine-koenig.org>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>