ARM: dts: dra72-evm: fix broken ethernet

With commit ceec08f5, phy is connected to slave 0, but
changing the phy node was missed, fix it by populating the
phy node to proper cpsw slave node.

Fixes: ceec08f5 ("ARM: dts: dra72-evm: Add mode-gpios entry for mac node")
Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Cc: Vignesh R <vigneshr@ti.com>
Tested-by: Tom Rini <trini@konsulko.com>