gru: fix handling of mesq failures

Fix endcase in handling GRU message queue failures due to NACKs of PUT
requests.  Must ensure that the "present" bits are cleared before
resending the message.

Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>