ASoC: wcd9xxx: Add check for array boundary

Current code does not check if the indexes of array
ch_h being accessed are within the maximum number of
channels that slimbus can have for the codec. The change
adds this check and ensures that indexes outside the
bounds of array are not accessed.

Change-Id: I3cd0e0daa14b86cbf718c00b8b2738d1f75150bd
CRs-fixed: 691820
Signed-off-by: Kuirong Wang <kuirongw@codeaurora.org>