net: phy: mscc: remove the TR CLK disable magic value

This patch adds a define for the 0x8000 magic value used to perform
enable/disable actions on the "token ring clock". The patch is only
cosmetic.

Signed-off-by: Quentin Schulz <quentin.schulz@bootlin.com>
Signed-off-by: Antoine Tenart <antoine.tenart@bootlin.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>