nfs: Fix nfs_parse_mount_options() kfree() leak

Fix a (small) memory leak in one of the error paths of the NFS mount
options parsing code.

Regression introduced in 2.6.30 by commit a67d18f (NFS: load the
rpc/rdma transport module automatically).

Reported-by: Yinghai Lu <[e-mail]>
Reported-by: Pekka Enberg <[e-mail]>
Signed-off-by: Ingo Molnar <[e-mail]>
Signed-off-by: Trond Myklebust <[e-mail]>
Cc: [e-mail]
Signed-off-by: Linus Torvalds <[e-mail]>

fs/nfs/super.c

···
 			default:
 				dfprintk(MOUNT, "NFS:   unrecognized "
 						"transport protocol\n");
+				kfree(string);
 				return 0;
 			}
 			break;