Bluetooth: audio: ascs: Fix handling zero Number_of_ASEs parameter

As per ASCS_v1.0
"A client-initiated ASE Control operation shall be defined as an
invalid length operation if the Number_of_ASEs parameter value is
less than 1".

Fixes: ASCS/SR/SPE/BI-{02,03,04,05,06}-C
Signed-off-by: Mariusz Skamra <mariusz.skamra@codecoup.pl>