NVMe: Remove outdated comments

The head can never overrun the tail since we won't allocate enough command
IDs to let that happen.  The status codes are in sync with the spec.
Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>

drivers/block/nvme.c

@@ -245,7 +245,6 @@ static int nvme_submit_cmd(struct nvme_queue *nvmeq, struct nvme_command *cmd)
 {
 	unsigned long flags;
 	u16 tail;
-	/* XXX: Need to check tail isn't going to overrun head */
 	spin_lock_irqsave(&nvmeq->q_lock, flags);
 	tail = nvmeq->sq_tail;
 	memcpy(&nvmeq->sq_cmds[tail], cmd, sizeof(*cmd));

include/linux/nvme.h

@@ -323,7 +323,6 @@ struct nvme_command {
 	};
 };
 
-/* XXX: Sync with spec */
 enum {
 	NVME_SC_SUCCESS			= 0x0,
 	NVME_SC_INVALID_OPCODE		= 0x1,