net: phy: ensure that phy IDs are correctly typed

PHY IDs are 32-bit unsigned quantities. Ensure that they are always
treated as such, and not passed around as "int"s.

Fixes: 13d0ab67 ("net: phy: check return code when requesting PHY driver module")
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>