mx_proc: Reduce linebuf size to 64 and fix comment

> pid + " (" comm + ") " + state + " " + pid + " \0"
> 10 + 2 + 15 + 2 + 1 + 1 + 10 + 2 = 43

Found-by: Donald

mx_proc.c

@@ -460,7 +460,7 @@ pid_t mx_proc_get_parent(pid_t pid) {
     FILE *statfile;
     pid_t parent;
     int n;
-    char linebuf[256];  // "2147483647 (max128chars) X 2147483647 " = 156
+    char linebuf[64];  // "2147483647 (max15chars) X 2147483647 " = 43
 
     if (pid == 0)       // no need to try /proc/0/stat
         return -1;