net: phy: realtek: net: Fix less than zero comparison of a u16

The comparisons of the u16 values priv->phycr1 and priv->phycr2 to less
than zero always false because they are unsigned. Fix this by using an
int for the assignment and less than zero check.

Addresses-Coverity: ("Unsigned compared against 0")
Fixes: 0a4355c2 ("net: phy: realtek: add dt property to disable CLKOUT clock")
Fixes: d90db36a ("net: phy: realtek: add dt property to enable ALDPS mode")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>