dtbhtool: Fix missing PATH_MAX macro from limits.h

Change-Id: Ie9cc147d6f4511d1fd696de7f8c58e01afdd079e
diff --git a/dtbhtool/mkbootimg.c b/dtbhtool/mkbootimg.c
index 7662591..4470fd2 100644
--- a/dtbhtool/mkbootimg.c
+++ b/dtbhtool/mkbootimg.c
@@ -25,6 +25,7 @@
 #include <unistd.h>
 #include <fcntl.h>
 #include <errno.h>
+#include <limits.h>
 
 #include <sys/types.h>
 #include <arpa/inet.h>