init/version.c: silence sparse warning by declaring the version string

Signed-off-by: NDaniel Guilak <daniel@danielguilak.com>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

init/version.c

@@ -16,6 +16,7 @@
 #define version(a) Version_ ## a
 #define version_string(a) version(a)
 
+extern int version_string(LINUX_VERSION_CODE);
 int version_string(LINUX_VERSION_CODE);
 
 struct uts_namespace init_uts_ns = {