IB/mthca: Fix thinko in mthca_table_find()

break only escapes from the innermost loop, and we want to escape both
loops and return an answer.  Noticed by Ishai Rabinovitch.

Signed-off-by: Michael S. Tsirkin <mst@mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>