nvme: reduce checks for zero command effects

For passthrough I/O commands, effects are usually to be zero.
nvme_passthrough_end() does three checks in futility for this case.
Bail out of function-call/checks.
Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/nvme/host/core.c

@@ -1137,7 +1137,8 @@ void nvme_execute_passthru_rq(struct request *rq)
 
 	effects = nvme_passthru_start(ctrl, ns, cmd->common.opcode);
 	blk_execute_rq(disk, rq, 0);
-	nvme_passthru_end(ctrl, effects);
+	if (effects) /* nothing to be done for zero cmd effects */
+		nvme_passthru_end(ctrl, effects);
 }
 EXPORT_SYMBOL_NS_GPL(nvme_execute_passthru_rq, NVME_TARGET_PASSTHRU);