net: mdio-mux: Remove unnecessary 'out of memory' message

This patch fix checkpatch warning about unnecessary 'out of memory'
message.

Signed-off-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>