media: mtk-cir: fix calculation of chk period

Since commit 528222d853f9 ("media: rc: harmonize infrared durations to
microseconds"), the calculation of the chk period is wrong. As a result,
all reported IR will have incorrect timings.

Now that the calculations are done in microseconds rather than nanoseconds,
we can fold the calculations in a simpler form with less rounding error.

Tested-by: Frank Wunderlich <[e-mail]>
Fixes: 528222d853f9 ("media: rc: harmonize infrared durations to microseconds")
Signed-off-by: Sean Young <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/rc/mtk-cir.c

···
 {
 	u32 val;
 
-	/* Period of raw software sampling in ns */
-	val = DIV_ROUND_CLOSEST(1000000000ul,
-				clk_get_rate(ir->bus) / ir->data->div);
-
 	/*
 	 * Period for software decoder used in the
 	 * unit of raw software sampling
 	 */
-	val = DIV_ROUND_CLOSEST(MTK_IR_SAMPLE, val);
+	val = DIV_ROUND_CLOSEST(clk_get_rate(ir->bus),
+				USEC_PER_SEC * ir->data->div / MTK_IR_SAMPLE);
 
 	dev_dbg(ir->dev, "@pwm clk  = \t%lu\n",
 		clk_get_rate(ir->bus) / ir->data->div);
···
 	mtk_irq_enable(ir, MTK_IRINT_EN);
 
 	dev_info(dev, "Initialized MT7623 IR driver, sample period = %dus\n",
-		 DIV_ROUND_CLOSEST(MTK_IR_SAMPLE, 1000));
+		 MTK_IR_SAMPLE);
 
 	return 0;