build system: fix generate_BUFSIZ.sh to not alternate 1k and malloc builds

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/Makefile b/Makefile
index 75a33c1..d595023 100644
--- a/Makefile
+++ b/Makefile
@@ -611,7 +611,7 @@
       "$(core-y)" \
       "$(libs-y)" \
       "$(LDLIBS)" \
-      && $(srctree)/scripts/generate_BUFSIZ.sh include/common_bufsiz.h
+      && $(srctree)/scripts/generate_BUFSIZ.sh --post include/common_bufsiz.h
 
 # Generate System.map
 quiet_cmd_sysmap = SYSMAP