ARM: dts: am437x-l4: fix compatible for cpsw switch dt node

Fix compatible the new CPSW switchdev DT node to avoid probing of legacy
CPSW driver which fails:
[    2.781009] cpsw 4a100000.switch: invalid resource

Fixes: 7bf8f37a ("ARM: dts: am437x-l4: add dt node for new cpsw switchdev driver")
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>