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: Pavel Emelyanov <xemul@openvz.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>