net: phy: mscc: remove unneeded temporary variable

Here, the rc variable is either used only for the condition right after
the assignment or right before being used as the return value of the
function it's being used in.

So let's remove this unneeded temporary variable whenever possible.

Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Quentin Schulz <quentin.schulz@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>