9p: Modify struct 9p_fid to use a kuid_t not a uid_t

Change struct 9p_fid and it's associated functions to
use kuid_t's instead of uid_t.

Cc: Eric Van Hensbergen <ericvh@gmail.com>
Cc: Ron Minnich <rminnich@gmail.com>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

fs/9p/v9fs.c

@@ -387,7 +387,7 @@ struct p9_fid *v9fs_session_init(struct v9fs_session_info *v9ses,
 	if ((v9ses->flags & V9FS_ACCESS_MASK) == V9FS_ACCESS_SINGLE)
 		fid->uid = v9ses->uid;
 	else
-		fid->uid = ~0;
+		fid->uid = INVALID_UID;
 
 #ifdef CONFIG_9P_FSCACHE
 	/* register the session for caching */