staging: dgnc: dgnc_cls.c: Replaced udelay by usleep_range

This patch is to file dgnc_cls.c that fixes up udelay function by
usleep_range.
It is safe to use according to the following documentation
Documentation/timers/timers-howto.txt. So that is why I have given
an appropriate time range.
Signed-off-by: NJitendra Kumar Khasdev <jkhasdev@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/dgnc/dgnc_cls.c

@@ -934,7 +934,7 @@ static void cls_flush_uart_write(struct channel_t *ch)
 
 	writeb((UART_FCR_ENABLE_FIFO | UART_FCR_CLEAR_XMIT),
 	       &ch->ch_cls_uart->isr_fcr);
-	udelay(10);
+	usleep_range(10, 20);
 
 	ch->ch_flags |= (CH_TX_FIFO_EMPTY | CH_TX_FIFO_LWM);
 }