IB/hfi1: Add a missing rcu_read_unlock()

This patch avoids that sparse reports the following:

drivers/infiniband/hw/hfi1/driver.c:251:13: warning: context imbalance in 'rcv_hdrerr' - different lock contexts for basic block
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Cc: Mike Marciniszyn <mike.marciniszyn@intel.com>
Cc: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/hfi1/driver.c

@@ -390,6 +390,7 @@ static void rcv_hdrerr(struct hfi1_ctxtdata *rcd, struct hfi1_pportdata *ppd,
 				svc_type = IB_CC_SVCTYPE_UC;
 				break;
 			default:
+				rcu_read_unlock();
 				goto drop;
 			}