kbuild: do not redirect the first prerequisite for filechk

Currently, filechk unconditionally opens the first prerequisite and
redirects it as the stdin of a filechk_* rule.  Hence, every target
using $(call filechk,...) must list something as the first prerequisite
even if it is unneeded.

'< $<' is actually unneeded in most cases.  Each rule can explicitly
adds it if necessary.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

scripts/Makefile.lib

@@ -415,7 +415,7 @@ define filechk_offsets
 	 echo " * This file was generated by Kbuild"; \
 	 echo " */"; \
 	 echo ""; \
-	 sed -ne $(sed-offsets); \
+	 sed -ne $(sed-offsets) < $<; \
 	 echo ""; \
 	 echo "#endif" )
 endef