net: dwc_eth_qos: Pass -1 to phy_connect() to scan for all PHYs

PHY address 0 is a valid PHY address, to scan for all PHYs, pass -1 to
phy_connect(). Passing 0 used to work before be accident, but does no
longer.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Joe Hershberger <joe.hershberger@ni.com>
Cc: Patrice Chotard <patrice.chotard@st.com>
Cc: Patrick Delaunay <patrick.delaunay@st.com>
Cc: Ramon Fried <rfried.dev@gmail.com>
Reviewed-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>