ASoC: wm_adsp: Fix theoretical NULL pointer for alg_region

ASoC: wm_adsp: Fix theoretical NULL pointer for alg_region

Fix potential NULL pointer dereference for alg_region in
wm_adsp_buffer_parse_legacy. In practice this can never happen as
loading the firmware should have failed at the wm_adsp2_setup_algs
stage, however probably better for the code to be robust against
future changes and this is more helpful for static analysis.

Signed-off-by: Li Xu <li.xu@cirrus.com>
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20191001130911.19238-1-ckeepax@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>