microblaze: Remove *.dtb files in make clean

dts/Makefile is called only for simpleImage target
which is causing that *.dtb are not removed.
This patch fix it.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
diff --git a/arch/microblaze/boot/Makefile b/arch/microblaze/boot/Makefile
index 8e211cc..91d2068 100644
--- a/arch/microblaze/boot/Makefile
+++ b/arch/microblaze/boot/Makefile
@@ -34,5 +34,4 @@
 	$(call if_changed,strip)
 	@echo 'Kernel: $@ is ready' ' (#'`cat .version`')'
 
-
-clean-files += simpleImage.*.unstrip linux.bin.ub
+clean-files += simpleImage.*.unstrip linux.bin.ub dts/*.dtb
diff --git a/arch/microblaze/boot/dts/Makefile b/arch/microblaze/boot/dts/Makefile
index c4982d1..a3d2e42 100644
--- a/arch/microblaze/boot/dts/Makefile
+++ b/arch/microblaze/boot/dts/Makefile
@@ -16,5 +16,3 @@
 
 # Rule to build device tree blobs
 DTC_FLAGS := -p 1024
-
-clean-files += *.dtb