ARM: dts: kirkwood: replace status value "ok" by "okay"

While the DT parser recognizes "ok" as a valid value for the
"status" property, it is actually mentioned nowhere. Use the
proper value "okay" instead, as done in the majority of files
already.

Signed-off-by: Adrian Schmutzler <freifunk@adrianschmutzler.de>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>