The error handling paths in mthca_tavor_post_srq_recv() and
mthca_arbel_post_srq_recv() are quite bogus, the result of a
screwed up merge.  Fix them so they work as intended.

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