usb: f_mass_storage: sleep_thread: decrease the interval for check ctrlc()

This change decreases the interval of calls to:
- display busy indicator
- check ctrlc()
- check cable connection

By this change, breaking the UMS command is more easy on Odroid XU3.

Signed-off-by: Inha Song <ideal.song@samsung.com>
Cc: Lukasz Majewski <l.majewski@samsung.com>
Cc: Marek Vasut <marex@denx.de>

drivers/usb/gadget/f_mass_storage.c

@@ -671,7 +671,7 @@ static int sleep_thread(struct fsg_common *common)
 		if (common->thread_wakeup_needed)
 			break;
 
-		if (++i == 50000) {
+		if (++i == 20000) {
 			busy_indicator();
 			i = 0;
 			k++;