net: designware: fix uninitialized phy_addr usage

When CONFIG_DW_SEARCH_PHY is disabled, the local phy_addr variable
never gets initialized which causes random behavior at runtime and a
gcc warning.  So set it by default to the stored phy address.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Reviewed-by: Vipin Kumar <vipin.kumar@st.com>

Fix commit message.
Signed-off-by: Wolfgang Denk <wd@denx.de>