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>
diff --git a/Makefile b/Makefile
index 433f870..bc3a65b 100644
--- a/Makefile
+++ b/Makefile
@@ -1117,7 +1117,7 @@
 	echo '#define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + (c))';)
 endef
 
-$(version_h): $(srctree)/Makefile FORCE
+$(version_h): FORCE
 	$(call filechk,version.h)
 	$(Q)rm -f $(old_version_h)