kbuild: KBUILD_VERBOSE was exported twice

This fixes http://bugzilla.kernel.org/show_bug.cgi?id=4727

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
---

Makefile

@@ -233,7 +233,7 @@ ifeq ($(MAKECMDGOALS),)
   KBUILD_MODULES := 1
 endif
 
-export KBUILD_MODULES KBUILD_BUILTIN KBUILD_VERBOSE
+export KBUILD_MODULES KBUILD_BUILTIN
 export KBUILD_CHECKSRC KBUILD_SRC KBUILD_EXTMOD
 
 # Beautify output