kbuild: pass dst= to Makefile.headersinst from top Makefile

We can always pass dst= from the top Makefile.  This will simplify
the logic in Makefile.headersinst.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/Makefile b/Makefile
index ce58756..70c414b 100644
--- a/Makefile
+++ b/Makefile
@@ -1154,7 +1154,7 @@
 headers_install: __headers
 	$(if $(wildcard $(srctree)/arch/$(hdr-arch)/include/uapi/asm/Kbuild),, \
 	  $(error Headers not exportable for the $(SRCARCH) architecture))
-	$(Q)$(MAKE) $(hdr-inst)=include/uapi
+	$(Q)$(MAKE) $(hdr-inst)=include/uapi dst=include
 	$(Q)$(MAKE) $(hdr-inst)=arch/$(hdr-arch)/include/uapi $(hdr-dst)
 
 PHONY += headers_check_all
@@ -1163,7 +1163,7 @@
 
 PHONY += headers_check
 headers_check: headers_install
-	$(Q)$(MAKE) $(hdr-inst)=include/uapi HDRCHECK=1
+	$(Q)$(MAKE) $(hdr-inst)=include/uapi dst=include HDRCHECK=1
 	$(Q)$(MAKE) $(hdr-inst)=arch/$(hdr-arch)/include/uapi $(hdr-dst) HDRCHECK=1
 
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