arm64: dts: imx: Fix imx8mm-kontron-n801x-s.dtb target

While running 'make dtbs_install', the following error occurs:

make[3]: *** No rule to make target 'rootfs/freescale/imx8mm-kontron-n801x-s.dts', needed by '__dtbs_install'.

It should be .dtb, not .dts.

Fixes: 8668d8b2 ("arm64: dts: Add the Kontron i.MX8M Mini SoMs and baseboards")
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/Makefile

@@ -32,7 +32,7 @@ dtb-$(CONFIG_ARCH_LAYERSCAPE) += fsl-lx2162a-qds.dtb
 dtb-$(CONFIG_ARCH_MXC) += imx8mm-beacon-kit.dtb
 dtb-$(CONFIG_ARCH_MXC) += imx8mm-evk.dtb
 dtb-$(CONFIG_ARCH_MXC) += imx8mm-ddr4-evk.dtb
-dtb-$(CONFIG_ARCH_MXC) += imx8mm-kontron-n801x-s.dts
+dtb-$(CONFIG_ARCH_MXC) += imx8mm-kontron-n801x-s.dtb
 dtb-$(CONFIG_ARCH_MXC) += imx8mm-var-som-symphony.dtb
 dtb-$(CONFIG_ARCH_MXC) += imx8mn-evk.dtb
 dtb-$(CONFIG_ARCH_MXC) += imx8mn-ddr4-evk.dtb