tree.sh: Don't run make-clean on dry runs

Otherwise, ./mk -d (without arguments) fails for GRUB,
which first requires running autoconf to get a Makefile.

Signed-off-by: Leah Rowe <leah@libreboot.org>

include/tree.sh

@@ -275,7 +275,8 @@ elfcheck()
 
 handle_makefile()
 {
-	$dry check_makefile "$srcdir" && x_ make -C "$srcdir" $cleanargs clean
+	$dry check_makefile "$srcdir" && \
+	    $dry x_ make -C "$srcdir" $cleanargs clean
 
 	[ -f "$defconfig" ] && x_ cp "$defconfig" "$srcdir/.config"
 	[ -n "$mode" ] || [ -n "$btype" ] || $dry make -C \