drivers: net: bcm-sf2: pass -1 to phy_connect()

Passing 0 to PHY connect used to trigger a MDIO scan due to a bug fixed in
the meantime.  It's unclear if bcm-sf2 wants to connect to PHY @ addr 0 or
is scanning the bus, passing -1 here should keep it functional either way.

Signed-off-by: Alex Marginean <alexandru.marginean@nxp.com>
Cc: Jiandong Zheng <jdzheng@broadcom.com>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>