kbuild: include limits.h in sumversion.c for PATH_MAX

POSIX says limits.h defines PATH_MAX so we should include it (which fixes
compiling on some systems like OS X).
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

scripts/mod/sumversion.c

@@ -7,6 +7,7 @@
 #include <ctype.h>
 #include <errno.h>
 #include <string.h>
+#include <limits.h>
 #include "modpost.h"
 
 /*