user32: Constify some variables.

dlls/user32/comm16.c

@@ -140,7 +140,7 @@ static struct DosDeviceStruct *GetDeviceStruct(int index)
 	return NULL;
 }
 
-static int    GetCommPort_ov(LPOVERLAPPED ov, int write)
+static int    GetCommPort_ov(const OVERLAPPED *ov, int write)
 {
 	int x;
 
@@ -161,13 +161,13 @@ static int WinError(void)
 		}
 }
 
-static unsigned comm_inbuf(struct DosDeviceStruct *ptr)
+static unsigned comm_inbuf(const struct DosDeviceStruct *ptr)
 {
   return ((ptr->ibuf_tail > ptr->ibuf_head) ? ptr->ibuf_size : 0)
     + ptr->ibuf_head - ptr->ibuf_tail;
 }
 
-static unsigned comm_outbuf(struct DosDeviceStruct *ptr)
+static unsigned comm_outbuf(const struct DosDeviceStruct *ptr)
 {
   return ((ptr->obuf_tail > ptr->obuf_head) ? ptr->obuf_size : 0)
     + ptr->obuf_head - ptr->obuf_tail;
@@ -360,7 +360,7 @@ static void comm_waitwrite(struct DosDeviceStruct *ptr)
 /*****************************************************************************
  *	COMM16_DCBtoDCB16	(Internal)
  */
-static INT16 COMM16_DCBtoDCB16(LPDCB lpdcb, LPDCB16 lpdcb16)
+static INT16 COMM16_DCBtoDCB16(const DCB *lpdcb, LPDCB16 lpdcb16)
 {
 	if(lpdcb->BaudRate<0x10000)
 		lpdcb16->BaudRate = lpdcb->BaudRate;