aice: use keep_alive() to avoid timeout warning messages

As polling $dbger, call keep_alive() to avoid timeout messages.

Change-Id: Ia03d90535c2bd6049763209194c21f70fd8b7e8b
Signed-off-by: Hsiangkai Wang <hsiangkai@gmail.com>
Reviewed-on: http://openocd.zylin.com/1566
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>

src/jtag/aice/aice_usb.c

@@ -1490,6 +1490,9 @@ static int aice_check_dbger(uint32_t expect_status)
 			return ERROR_OK;
 		}
 
+		if ((i % 30) == 0)
+			keep_alive();
+
 		long long then = 0;
 		if (i == aice_count_to_check_dbger)
 			then = timeval_ms();