ASoC: msm: Change wsa dt property to optional

Make wsa max number of devices to optional
so that it can be removed or set to 0 if wsa
is not used and still continue with the sound card
enumeration.

CRs-fixed: 2060360
Change-Id: I30b8cca561bbcfe2bd2221d17659960ab9db27b6
Signed-off-by: Karthikeyan Mani <kmani@codeaurora.org>