ARM: imx: Update MAINTAINERS file globs for i.MX6 DHSOM

Update the MAINTAINERS file glob to cover all of i.MX6 DHSOM related files.

Signed-off-by: Marek Vasut <marex@denx.de>

board/dhelectronics/dh_imx6/MAINTAINERS

@@ -3,6 +3,5 @@ M:	Andreas Geisreiter <ageisreiter@dh-electronics.de>
 M:	Christoph Niedermaier <cniedermaier@dh-electronics.com>
 L:	u-boot@dh-electronics.com
 S:	Maintained
-F:	board/dhelectronics/dh_imx6/
-F:	include/configs/dh_imx6.h
-F:	configs/dh_imx6_defconfig
+N:	imx6.*dh[cs]o
+N:	dh_imx6