uml: remove TOPDIR

TOPDIR is obsolete, use srctree instead.  This patch removes TOPDIR from all
UML Makefiles.

Cc: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: WANG Cong <xiyou.wangcong@gmail.com>
Signed-off-by: Jeff Dike <jdike@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/arch/um/Makefile b/arch/um/Makefile
index fb8854a..cb4af9b 100644
--- a/arch/um/Makefile
+++ b/arch/um/Makefile
@@ -160,7 +160,7 @@
 	$(Q)mkdir -p $(objtree)/include/asm-um
 	$(Q)ln -fsn $(srctree)/include/asm-um/$(basename $(notdir $@))-$(SUBARCH)$(suffix $@) $@
 else
-	$(Q)cd $(TOPDIR)/$(dir $@) ; \
+	$(Q)cd $(srctree)/$(dir $@) ; \
 	ln -sf $(basename $(notdir $@))-$(SUBARCH)$(suffix $@) $(notdir $@)
 endif
 
@@ -170,7 +170,7 @@
 	$(Q)mkdir -p $(objtree)/include/asm-um
 	$(Q)ln -fsn $(srctree)/include/asm-$(HEADER_ARCH) include/asm-um/arch
 else
-	$(Q)cd $(TOPDIR)/include/asm-um && ln -fsn ../asm-$(HEADER_ARCH) arch
+	$(Q)cd $(srctree)/include/asm-um && ln -fsn ../asm-$(HEADER_ARCH) arch
 endif
 
 $(objtree)/$(ARCH_DIR)/include: