IB/ehca: Serialize hypervisor calls in ehca_register_mr()

Some pSeries hypervisor versions show a race condition in the allocate
MR hCall.  Serialize this call per adapter to circumvent this problem.

Signed-off-by: Joachim Fenkes <fenkes@de.ibm.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>
diff --git a/drivers/infiniband/hw/ehca/ehca_classes.h b/drivers/infiniband/hw/ehca/ehca_classes.h
index f64d42b..1d286d3 100644
--- a/drivers/infiniband/hw/ehca/ehca_classes.h
+++ b/drivers/infiniband/hw/ehca/ehca_classes.h
@@ -277,6 +277,7 @@
 
 extern spinlock_t ehca_qp_idr_lock;
 extern spinlock_t ehca_cq_idr_lock;
+extern spinlock_t hcall_lock;
 extern struct idr ehca_qp_idr;
 extern struct idr ehca_cq_idr;