Bluetooth: Controller: Fix extended scanning assertion

Fix extended scanning assertion after long duration.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>
(cherry picked from commit ac39ad724911d79557fd12b40b085ab639fca173)
diff --git a/subsys/bluetooth/controller/ll_sw/nordic/lll/lll_scan.c b/subsys/bluetooth/controller/ll_sw/nordic/lll/lll_scan.c
index 6cb4895..eaafd88 100644
--- a/subsys/bluetooth/controller/ll_sw/nordic/lll/lll_scan.c
+++ b/subsys/bluetooth/controller/ll_sw/nordic/lll/lll_scan.c
@@ -921,11 +921,11 @@
 	}
 	lll_chan_set(37 + lll->chan);
 
+#if defined(CONFIG_BT_CENTRAL) || defined(CONFIG_BT_CTLR_ADV_EXT)
 #if defined(CONFIG_BT_CENTRAL)
 	bool is_sched_advanced = IS_ENABLED(CONFIG_BT_CTLR_SCHED_ADVANCED) &&
 				 lll->conn && lll->conn_win_offset_us;
 	uint32_t ticks_anchor_prev;
-	uint32_t ticks_at_start;
 
 	if (is_sched_advanced) {
 		/* Get the ticks_anchor when the offset to free time space for
@@ -938,14 +938,17 @@
 	} else {
 		ticks_anchor_prev = 0U;
 	}
+#endif /* CONFIG_BT_CENTRAL */
+
+	uint32_t ticks_at_start;
 
 	ticks_at_start = ticker_ticks_now_get() +
 			 HAL_TICKER_CNTR_CMP_OFFSET_MIN;
 	remainder_us = radio_tmr_start_tick(0, ticks_at_start);
-#else /* !CONFIG_BT_CENTRAL */
+#else /* !CONFIG_BT_CENTRAL && !CONFIG_BT_CTLR_ADV_EXT */
 
 	remainder_us = radio_tmr_start_now(0);
-#endif /* !CONFIG_BT_CENTRAL */
+#endif /* !CONFIG_BT_CENTRAL && !CONFIG_BT_CTLR_ADV_EXT */
 
 	/* capture end of Rx-ed PDU, for initiator to calculate first
 	 * central event.