ASoC: codecs: lpass-wsa-macro: handle unexpected input

ASoC: codecs: lpass-wsa-macro: handle unexpected input

Static analysis reports this problem

lpass-wsa-macro.c:1732:6: warning: Array subscript is undefined
        if (wsa->ec_hq[ec_tx]) {
            ^~~~~~~~~~~~~~~~~

The happens because 'ec_tx' is never initialized and there is
no default in switch statement that sets ec_tx.  Add a default
case that returns an error before the array is accessed.

Signed-off-by: Tom Rix <trix@redhat.com>
Reviewed-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20210430142117.3272772-1-trix@redhat.com
Signed-off-by: Mark Brown <broonie@kernel.org>