stmmac: fix phy naming inconsistency

After commit "db8857bf stmmac: use an unique MDIO bus name" my
device stopped being probed because two different names were being
used in different places. This fixes the inconsistency.

Signed-off-by: Alessandro Rubini <rubini@gnudd.com>
Acked-by: Giancarlo Asnaghi <giancarlo.asnaghi@st.com>
Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Cc: Florian Fainelli <florian@openwrt.org>
Acked-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: David S. Miller <davem@davemloft.net>