make: fix clean target

Before this patch when running `make clean` we get:

    make: *** No rule to make target 'rm', needed by 'clean'.  Stop.

Signed-off-by: Alexandre Perrin <[email protected]>

Author: kaworu

Makefile

@@ -14,4 +14,5 @@ github-actions:
 local: github-actions
 	strip github-actions
 
-clean: rm -fr github-actions
+clean:
+	rm -fr github-actions