sparc: vdso: add FORCE to the build rule of %.so

$(call if_changed,...) must have FORCE as a prerequisite.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/sparc/vdso/Makefile

@@ -68,7 +68,7 @@ CFLAGS_REMOVE_vdso-note.o = -pg
 CFLAGS_REMOVE_vclock_gettime.o = -pg
 
 $(obj)/%.so: OBJCOPYFLAGS := -S
-$(obj)/%.so: $(obj)/%.so.dbg
+$(obj)/%.so: $(obj)/%.so.dbg FORCE
 	$(call if_changed,objcopy)
 
 CPPFLAGS_vdso32.lds = $(CPPFLAGS_vdso.lds)