remove useless comments in dma

This comment is useless, just removes it and makes the codes clear.

Signed-off-by: Wanpeng Li <liwp@linux.vnet.ibm.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

dma.h

@@ -11,7 +11,6 @@
 #define DMA_H
 
 #include <stdio.h>
-//#include "cpu.h"
 #include "hw/hw.h"
 #include "block.h"