initd: fix off-by-one error in mkdev.c

Actually make sure buffer is 0-terminated intead of writing the 0-byte
out of bounds.

Coverity CID: 1330087 Readlink used insecurely
Signed-off-by: Daniel Golle <daniel@makrotopia.org>

initd/mkdev.c

@@ -86,7 +86,7 @@ static void find_devs(bool block)
 		if (len <= 0)
 			continue;
 
-		buf[len] = 0;
+		buf[sizeof(buf) - 1] = '\0';
 		if (!find_pattern(buf))
 			continue;