staging: dgnc: Fix usleep_range is preferred over udelay

This patch fixes the issue:

CHECK: usleep_range is preferred over udelay; see
Documentation/timers/timers-howto.txt
Signed-off-by: Joshua Abraham <j.abraham1776@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/dgnc/dgnc_cls.c

@@ -397,7 +397,7 @@ static void cls_assert_modem_signals(struct channel_t *ch)
 	writeb(out, &ch->ch_cls_uart->mcr);
 
 	/* Give time for the UART to actually drop the signals */
-	udelay(10);
+	usleep_range(10, 20);
 }
 
 static void cls_copy_data_from_queue_to_uart(struct channel_t *ch)