MAINTAINERS: oxnas: Add new files definitions

Fix the dts files maintained by the OXNAS platform, add a new board.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>

MAINTAINERS

@@ -1478,8 +1478,9 @@ L:	linux-arm-kernel@lists.infradead.org (moderated for non-subscribers)
 L:	linux-oxnas@lists.tuxfamily.org (moderated for non-subscribers)
 S:	Maintained
 F:	arch/arm/mach-oxnas/
-F:	arch/arm/boot/dts/oxnas*
+F:	arch/arm/boot/dts/ox8*.dtsi
 F:	arch/arm/boot/dts/wd-mbwe.dts
+F:	arch/arm/boot/dts/cloudengines-pogoplug-series-3.dts
 N:	oxnas
 
 ARM/Mediatek RTC DRIVER