frv: use find_task_by_vpid in cxn_pin_by_pid

The function is question gets the pid from sysctl table, so this one is a
virtual pid, i.e.  the pid of a task as it is seen from inside a namespace.

So the find_task_by_vpid() must be used here.
Signed-off-by: NPavel Emelyanov <xemul@openvz.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/frv/mm/mmu-context.c

@@ -181,7 +181,7 @@ int cxn_pin_by_pid(pid_t pid)
 
 	/* get a handle on the mm_struct */
 	read_lock(&tasklist_lock);
-	tsk = find_task_by_pid(pid);
+	tsk = find_task_by_vpid(pid);
 	if (tsk) {
 		ret = -EINVAL;