input: ixp4xx-beeper: don't use symbols from <mach/timex.h>

mach/timex.h is about to be dropped so don't use symbols defined in
there. For ixp4xx there is a suitable substitute for IXP4XX_TIMER_FREQ,
i.e. a global and exported variable that holds the same value.
Acked-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: NUwe Kleine-König <u.kleine-koenig@pengutronix.de>

drivers/input/misc/ixp4xx-beeper.c

@@ -67,7 +67,7 @@ static int ixp4xx_spkr_event(struct input_dev *dev, unsigned int type, unsigned
 	}
 
 	if (value > 20 && value < 32767)
-		count = (IXP4XX_TIMER_FREQ / (value * 4)) - 1;
+		count = (ixp4xx_timer_freq / (value * 4)) - 1;
 
 	ixp4xx_spkr_control(pin, count);