net: bcmgenet: Fix speed selection for reverse MII

The phy supported speed is being used to determine if the MAC should
be configured to 100 or 1G. The masking logic is broken. Instead, look
at 1G supported speeds to enable 1G MAC support.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>