fs/proc/root.c: use NULL instead of 0 for pointer

This cleanup also fixes the following sparse warning:

  fs/proc/root.c:64:45: warning: Using plain integer as NULL pointer
Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/proc/root.c

@@ -61,7 +61,7 @@ static int proc_parse_options(char *options, struct pid_namespace *pid)
 		if (!*p)
 			continue;
 
-		args[0].to = args[0].from = 0;
+		args[0].to = args[0].from = NULL;
 		token = match_token(p, tokens, args);
 		switch (token) {
 		case Opt_gid: