tools/counter: Makefile: Replace rmdir by rm to avoid make,clean failure

Use rm -df instead of rmdir -p since rmdir requires the directory exist
so it causes "make -C tools clean" failed if someone only builds other
tools but not counter.

Fixes: 228354ed ("tools/counter: Makefile: Remove lingering 'include' directories on make clean")
Signed-off-by: Anh Tuan Phan <tuananhlfc@gmail.com>
Link: https://lore.kernel.org/r/d4080db5-1825-2848-079a-8bb674d8ee44@gmail.com/Signed-off-by: William Breathitt Gray <william.gray@linaro.org>

tools/counter/Makefile

@@ -40,7 +40,8 @@ $(OUTPUT)counter_example: $(COUNTER_EXAMPLE)
 clean:
 	rm -f $(ALL_PROGRAMS)
 	rm -rf $(OUTPUT)include/linux/counter.h
-	rmdir -p $(OUTPUT)include/linux
+	rm -df $(OUTPUT)include/linux
+	rm -df $(OUTPUT)include
 	find $(or $(OUTPUT),.) -name '*.o' -delete -o -name '\.*.d' -delete
 
 install: $(ALL_PROGRAMS)