IB/hfi1: Fix user SDMA racy user request claim

The user SDMA in-use claim bit is in the structure that gets zeroed out
once the claim is made.  Move the request in-use flag into its own bit
array and use that for atomic claims.  This cleans up the claim code and
removes any race possibility.

Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Dean Luick <dean.luick@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/hw/hfi1/user_sdma.h

@@ -63,6 +63,7 @@ struct hfi1_user_sdma_pkt_q {
 	struct hfi1_devdata *dd;
 	struct kmem_cache *txreq_cache;
 	struct user_sdma_request *reqs;
+	unsigned long *req_in_use;
 	struct iowait busy;
 	unsigned state;
 	wait_queue_head_t wait;