cbfstool: off-by-one on the gcc version that provides _Static_assert

According to https://gcc.gnu.org/gcc-4.6/changes.html it's only in gcc 4.6,
not 4.5, which I mistakenly believed.

Change-Id: I8212e7921bd9d1436a0ba491cbe6c4d473228956
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: http://review.coreboot.org/11476
Reviewed-by: Jonathan A. Kollasch <jakllsch@kollasch.net>
Tested-by: build bot (Jenkins)
diff --git a/util/cbfstool/cbfs.h b/util/cbfstool/cbfs.h
index d1b97c5..f738c60 100644
--- a/util/cbfstool/cbfs.h
+++ b/util/cbfstool/cbfs.h
@@ -88,7 +88,7 @@
 	char filename[];
 } __PACKED;
 
-#if defined __GNUC__ && (__GNUC__ * 100 + __GNUC_MINOR__) >= 405
+#if defined __GNUC__ && (__GNUC__ * 100 + __GNUC_MINOR__) >= 406
 _Static_assert(sizeof(struct cbfs_file) == 24, "cbfs_file size mismatch");
 #endif