driver: timer: stm32_lptim: tickless mode without a compilation flag

In the timeout function, remove the compilation flag
and use the macro instead.

Signed-off-by: Francois Ramu <francois.ramu@st.com>
diff --git a/drivers/timer/stm32_lptim_timer.c b/drivers/timer/stm32_lptim_timer.c
index 09fae75..5ca5ebf 100644
--- a/drivers/timer/stm32_lptim_timer.c
+++ b/drivers/timer/stm32_lptim_timer.c
@@ -178,12 +178,15 @@
 
 void z_clock_set_timeout(s32_t ticks, bool idle)
 {
-#ifdef CONFIG_TICKLESS_KERNEL
 	/* new LPTIM1 AutoReload value to set (aligned on Kernel ticks) */
 	u32_t next_arr = 0;
 
 	ARG_UNUSED(idle);
 
+	if (!IS_ENABLED(CONFIG_TICKLESS_KERNEL)) {
+		return;
+	}
+
 	/* ARROK bit validates previous write operation to ARR register */
 	while (LL_LPTIM_IsActiveFlag_ARROK(LPTIM1) == 0) {
 	}
@@ -247,8 +250,6 @@
 	LL_LPTIM_SetAutoReload(LPTIM1, next_arr);
 
 	k_spin_unlock(&lock, key);
-
-#endif /* CONFIG_TICKLESS_KERNEL */
 }
 
 u32_t z_clock_elapsed(void)