bluetooth: Fix slimbus shutdown sequence

During slimbus shutdown process, registered codec
driver callback has been implemented in wrong seqeunce.
So, it causes audio data overflow and impact on next
audio streaming. To correct the sequence, slimbus port
disable routine should be performed when WCN codec shutdown
callback is called.

Change-Id: Id6ef22c34066adbb5b28bc31e605776c467bf03c
Signed-off-by: Sungjun Park <sjpark@codeaurora.org>