ARM: dts: am335x-baltos-ir5221: fix cpsw_emac0 link type

In Baltos iR5221 cpsw_emac0 is connected directly to the switch IC and
hence needs to be configured as "fixed-link".

Signed-off-by: Yegor Yefremov <yegorslists@googlemail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Tony Lindgren <tony@atomide.com>