net: phy: set devices_in_package only after validation

Only set the devices_in_package to a non-zero value if we find a valid
value for this field, so we avoid leaving it set to e.g. 0x1fffffff.

Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>