Bluetooth: controller: Revert cleanup redundant ticker busy loop

This reverts commit 698de889 ("Bluetooth: controller:
Cleanup redundant ticker busy loop")

Scan enable asserted in ctrl.c line 3756 due to the fact that a
role event was active and ticker job has hence been disabled.
Add back the busy loop so that scan enable can wait until the
active role event completes gracefully.

The ticker busy loop is mandatory in all ticker interface calls
if a blocking behavior is desired.

Signed-off-by: Vinayak Kariappa Chettimada <vich@nordicsemi.no>