i2c: riic: Use predefined macro and simplify clock tick calculation

Replace the hardcoded `1000000000` with the predefined `NSEC_PER_SEC`
macro for clarity. Simplify the code by introducing a `ns_per_tick`
variable to store `NSEC_PER_SEC / rate`, reducing redundancy and
improving readability.

Signed-off-by: Lad Prabhakar <[e-mail]>
Reviewed-by: Geert Uytterhoeven <[e-mail]>
Tested-by: Wolfram Sang <[e-mail]>
Reviewed-by: Wolfram Sang <[e-mail]>
Reviewed-by: Andy Shevchenko <[e-mail]>
Signed-off-by: Wolfram Sang <[e-mail]>

drivers/i2c/busses/i2c-riic.c

···
 #include <linux/platform_device.h>
 #include <linux/pm_runtime.h>
 #include <linux/reset.h>
+#include <linux/time.h>
 
 #define ICCR1_ICE	BIT(7)
 #define ICCR1_IICRST	BIT(6)
···
 {
 	int ret;
 	unsigned long rate;
+	unsigned long ns_per_tick;
 	int total_ticks, cks, brl, brh;
 	struct i2c_timings *t = &riic->i2c_t;
 	struct device *dev = riic->adapter.dev.parent;
···
 	 * Remove clock ticks for rise and fall times. Convert ns to clock
 	 * ticks.
 	 */
-	brl -= t->scl_fall_ns / (1000000000 / rate);
-	brh -= t->scl_rise_ns / (1000000000 / rate);
+	ns_per_tick = NSEC_PER_SEC / rate;
+	brl -= t->scl_fall_ns / ns_per_tick;
+	brh -= t->scl_rise_ns / ns_per_tick;
 
 	/* Adjust for min register values for when SCLE=1 and NFE=1 */
 	if (brl < 1)
···
 
 	pr_debug("i2c-riic: freq=%lu, duty=%d, fall=%lu, rise=%lu, cks=%d, brl=%d, brh=%d\n",
 		 rate / total_ticks, ((brl + 3) * 100) / (brl + brh + 6),
-		 t->scl_fall_ns / (1000000000 / rate),
-		 t->scl_rise_ns / (1000000000 / rate), cks, brl, brh);
+		 t->scl_fall_ns / ns_per_tick, t->scl_rise_ns / ns_per_tick, cks, brl, brh);
 
 	ret = pm_runtime_resume_and_get(dev);
 	if (ret)