NVMe: Remove outdated comments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>
diff --git a/drivers/block/nvme.c b/drivers/block/nvme.c
index 740a9c1..d4f95eb 100644
--- a/drivers/block/nvme.c
+++ b/drivers/block/nvme.c
@@ -245,7 +245,6 @@
 {
 	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));
diff --git a/include/linux/nvme.h b/include/linux/nvme.h
index c46a9b7..6b5a8d1 100644
--- a/include/linux/nvme.h
+++ b/include/linux/nvme.h
@@ -323,7 +323,6 @@
 	};
 };
 
-/* XXX: Sync with spec */
 enum {
 	NVME_SC_SUCCESS			= 0x0,
 	NVME_SC_INVALID_OPCODE		= 0x1,