nvme: remove CC register read-back during enabling

Any non-posted read should flush the previous write, so we don't
necessarily need to read back the value we just wrote. I've found at
least some controllers that respond with 0 for short moments after
writing the CC register with EN (enable) cleared, so the read-back is
overwriting our valid ctrl_config value and ends up breaking on the
subsequent enabling.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Keith Busch <kbusch@kernel.org>

drivers/nvme/host/core.c

@@ -2468,11 +2468,6 @@ int nvme_enable_ctrl(struct nvme_ctrl *ctrl)
 	if (ret)
 		return ret;
 
-	/* Flush write to device (required if transport is PCI) */
-	ret = ctrl->ops->reg_read32(ctrl, NVME_REG_CC, &ctrl->ctrl_config);
-	if (ret)
-		return ret;
-
 	/* CAP value may change after initial CC write */
 	ret = ctrl->ops->reg_read64(ctrl, NVME_REG_CAP, &ctrl->cap);
 	if (ret)