kbuild: make multi_depend work with targets in subdirectory

Precisely speaking, when you get the stem of the path, you should use
$(patsubst $(obj)/%,%,...) instead of $(notdir ...).

I do not see this usecase, but if you create a composite object in a
subdirectory, the Makefile should look like this:

   obj-$(CONFIG_FOO) += dir/foo.o
   dir/foo-objs      := dir/foo1.o dir/foo2.o

The member objects should be assigned to dir/foo-objs instead of
foo-objs.

This syntax is more consistent with commit 54b8ae66ae ("kbuild:
change *FLAGS_<basetarget>.o to take the path relative to $(obj)").

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

scripts/Makefile.lib

@@ -236,9 +236,9 @@ endif
 # Usage:
 #   $(call multi_depend, multi_used_targets, suffix_to_remove, suffix_to_add)
 define multi_depend
-$(foreach m, $(notdir $1), \
-	$(eval $(obj)/$m: \
-	$(addprefix $(obj)/, $(call suffix-search, $m, $2, $3))))
+$(foreach m, $1, \
+	$(eval $m: \
+	$(addprefix $(obj)/, $(call suffix-search, $(patsubst $(obj)/%,%,$m), $2, $3))))
 endef
 
 # Copy a file