arm64: dts: broadcom: Use the .dtb name in the rule, rather than .dts

Commit a7eb2639 ("arm64: dts: broadcom: Add reference to Compute
Module IO Board V3") adds the bcm2837-rpi-cm3-io3.dts file as a target
in the Makefile, rather than the .dtb name. This will skip the
generation of the .dtb file at compile time and will fail the dtbs_install
target.

Fixes: a7eb2639 ("arm64: dts: broadcom: Add reference to Compute Module IO Board V3")
Signed-off-by: Liviu Dudau <liviu@dudau.co.uk>
Acked-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Olof Johansson <olof@lixom.net>

arch/arm64/boot/dts/broadcom/Makefile

 # SPDX-License-Identifier: GPL-2.0
 dtb-$(CONFIG_ARCH_BCM2835) += bcm2837-rpi-3-b.dtb \
 			      bcm2837-rpi-3-b-plus.dtb \
-			      bcm2837-rpi-cm3-io3.dts
+			      bcm2837-rpi-cm3-io3.dtb
 
 subdir-y	+= northstar2
 subdir-y	+= stingray