[GFS2] match plock result with correct request

When the result of a posix lock request is read it needs to be matched up
with the correct waiting request.  The owner field needs to be used in the
comparison since more than one process may be waiting for locks on the
same file.

Signed-off-by: David Teigland <teigland@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>