Bluetooth: audio: ascs: Fix possible race condition

This fixes possible ASE state race condition. The notification is sent
immediately once the ASE state changed that eliminates a situation where
the state was changed by user action (API function call) when the state
was not yet notified to the remote Unicast Client.

Fixes: BAP/USR/SCC/BV-158-C
Signed-off-by: Mariusz Skamra <mariusz.skamra@codecoup.pl>