IB/ehca: Release mutex in error path of alloc_small_queue_page()

The pd->lock mutex is released on a successful return, so it should be
released on an error return as well.

The semantic patch that makes this change is as follows:
(http://www.emn.fr/x-info/coccinelle/)

// <smpl>
@@
expression l;
@@

mutex_lock(l);
... when != mutex_unlock(l)
    when any
    when strict
(
if (...) { ... when != mutex_unlock(l)
+   mutex_unlock(l);
    return ...;
}
|
mutex_unlock(l);
)
// </smpl>
Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/hw/ehca/ipz_pt_fn.c

@@ -163,6 +163,7 @@ static int alloc_small_queue_page(struct ipz_queue *queue, struct ehca_pd *pd)
 
 out:
 	ehca_err(pd->ib_pd.device, "failed to allocate small queue page");
+	mutex_unlock(&pd->lock);
 	return 0;
 }