net: phy: bcm7xxx: only show PHY revision once

bcm7xxx_28nm_config_init() can be called as frequently as needed by the
PHY library upon suspend/resume cycles and interface bring up/down, just
print the PHY revision once and for all in order not to spam kernel
logs.

Fixes: d8ebfed3f11b ("net: phy: bcm7xxx: utilize PHY revision in config_init")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>