blk-mq: don't handle failure in .get_budget

It is enough to just check if we can get the budget via .get_budget().
And we don't need to deal with device state change in .get_budget().

For SCSI, one issue to be fixed is that we have to call
scsi_mq_uninit_cmd() to free allocated ressources if SCSI device fails
to handle the request. And it isn't enough to simply call
blk_mq_end_request() to do that if this request is marked as
RQF_DONTPREP.

Fixes: 0df21c86bdbf(scsi: implement .get_budget and .put_budget for blk-mq)
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index 7775f6b..13a27d4 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -94,23 +94,18 @@ static void blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
 
 	do {
 		struct request *rq;
-		blk_status_t ret;
 
 		if (e->type->ops.mq.has_work &&
 				!e->type->ops.mq.has_work(hctx))
 			break;
 
-		ret = blk_mq_get_dispatch_budget(hctx);
-		if (ret == BLK_STS_RESOURCE)
+		if (!blk_mq_get_dispatch_budget(hctx))
 			break;
 
 		rq = e->type->ops.mq.dispatch_request(hctx);
 		if (!rq) {
 			blk_mq_put_dispatch_budget(hctx);
 			break;
-		} else if (ret != BLK_STS_OK) {
-			blk_mq_end_request(rq, ret);
-			continue;
 		}
 
 		/*
@@ -146,22 +141,17 @@ static void blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
 
 	do {
 		struct request *rq;
-		blk_status_t ret;
 
 		if (!sbitmap_any_bit_set(&hctx->ctx_map))
 			break;
 
-		ret = blk_mq_get_dispatch_budget(hctx);
-		if (ret == BLK_STS_RESOURCE)
+		if (!blk_mq_get_dispatch_budget(hctx))
 			break;
 
 		rq = blk_mq_dequeue_from_ctx(hctx, ctx);
 		if (!rq) {
 			blk_mq_put_dispatch_budget(hctx);
 			break;
-		} else if (ret != BLK_STS_OK) {
-			blk_mq_end_request(rq, ret);
-			continue;
 		}
 
 		/*