LeAudio: Fix Long Write in Control Point

The type of the write procedure is being handled by the stack depending on the MTU size.
Before the change, the GATT Client would have to handle it by itself.

Bug: 390583242
Test: mmm packages/modules/Bluetooth
Flags: Exempt, day to day fix
Change-Id: Id3ac544995fabe425c96ae1bb28b5b231af2778d