tty: imx, use ms_to_ktime

This really eliminates multiplications from the assembly. I would have
thought they are optimized by inlining ktime_set, but not on x86_64 with
gcc 10.

Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Pengutronix Kernel Team <kernel@pengutronix.de>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: NXP Linux Team <linux-imx@nxp.com>
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20210302062214.29627-10-jslaby@suse.czSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/imx.c

@@ -394,11 +394,7 @@ static void imx_uart_rts_inactive(struct imx_port *sport, u32 *ucr2)
 
 static void start_hrtimer_ms(struct hrtimer *hrt, unsigned long msec)
 {
-       long sec = msec / MSEC_PER_SEC;
-       long nsec = (msec % MSEC_PER_SEC) * 1000000;
-       ktime_t t = ktime_set(sec, nsec);
-
-       hrtimer_start(hrt, t, HRTIMER_MODE_REL);
+       hrtimer_start(hrt, ms_to_ktime(msec), HRTIMER_MODE_REL);
 }
 
 /* called with port.lock taken and irqs off */