NVMe: add TODO comment suggested by @sdongles

drivers/nvme/nvme.asm

@@ -1136,6 +1136,12 @@ proc cqyhdbl_write stdcall, pci:dword, y:dword, cqh:dword
 	mov 	word [esi + edx], ax ; Write to CQyHDBL
 	mov 	word [edi + NVM_QUEUE_ENTRY.head], ax
 
+	; NOTE: Currently commented out since we're just using
+	; plain spinlocks for notifying when a command has been
+	; completed, but this will be uncommented later and use
+	; semaphores instead of mutexes once the polling code
+	; has been replaced with the asynchronous API.
+
 	; Unlock the mutex now that the command is complete
 	;mov 	edi, dword [edi + NVM_QUEUE_ENTRY.cmd_ptr]
 	;mov 	ecx, [cqh]