net: phy: icplus: use the BIT macro where possible

This makes the code consistent by using the BIT() macro instead of
manual bit-shifting for some of the fields. No functional changes.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>