Bluetooth: controller: Fix cond compile of DLU event generation

Fix the conditional compile of Data Length Update event
generation on PHY Update Procedure when Data Length
Extensions are not supported.

The regression was introduced in
commit 70a89876 ("Bluetooth: controller: Fix missing
data length update event")

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