net/9p: Fix crash due to bad mount parameters.

It is not safe to use match_int without checking the token type returned
by match_token (especially when the token type returned is Opt_err and
args is empty). Fix it.
Signed-off-by: Abhishek Kulkarni <adkulkar@umail.iu.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/9p/trans_fd.c

@@ -735,12 +735,14 @@ static int parse_opts(char *params, struct p9_fd_opts *opts)
 		if (!*p)
 			continue;
 		token = match_token(p, tokens, args);
-		r = match_int(&args[0], &option);
-		if (r < 0) {
-			P9_DPRINTK(P9_DEBUG_ERROR,
-			 "integer field, but no integer?\n");
-			ret = r;
-			continue;
+		if (token != Opt_err) {
+			r = match_int(&args[0], &option);
+			if (r < 0) {
+				P9_DPRINTK(P9_DEBUG_ERROR,
+				"integer field, but no integer?\n");
+				ret = r;
+				continue;
+			}
 		}
 		switch (token) {
 		case Opt_port: