fs/9p: change simple_strtol to simple_strtoul

Since v9ses->uid is unsigned, it would seem better to use simple_strtoul that
simple_strtol.

A simplified version of the semantic patch that makes this change is as
follows: (http://www.emn.fr/x-info/coccinelle/)

// <smpl>
@r2@
long e;
position p;
@@

e = simple_strtol@p(...)

@@
position p != r2.p;
type T;
T e;
@@

e =
- simple_strtol@p
+ simple_strtoul
  (...)
// </smpl>
Signed-off-by: NJulia Lawall <julia@diku.dk>
Acked-by: NEric Van Hensbergen <ericvh@gmail.com>

fs/9p/v9fs.c

@@ -160,7 +160,7 @@ static int v9fs_parse_options(struct v9fs_session_info *v9ses)
 				v9ses->flags |= V9FS_ACCESS_ANY;
 			else {
 				v9ses->flags |= V9FS_ACCESS_SINGLE;
-				v9ses->uid = simple_strtol(s, &e, 10);
+				v9ses->uid = simple_strtoul(s, &e, 10);
 				if (*e != '\0')
 					v9ses->uid = ~0;
 			}