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.comSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/codecs/wm_adsp.c

@@ -3697,11 +3697,16 @@ static int wm_adsp_buffer_parse_legacy(struct wm_adsp *dsp)
 	u32 xmalg, addr, magic;
 	int i, ret;
 
+	alg_region = wm_adsp_find_alg_region(dsp, WMFW_ADSP2_XM, dsp->fw_id);
+	if (!alg_region) {
+		adsp_err(dsp, "No algorithm region found\n");
+		return -EINVAL;
+	}
+
 	buf = wm_adsp_buffer_alloc(dsp);
 	if (!buf)
 		return -ENOMEM;
 
-	alg_region = wm_adsp_find_alg_region(dsp, WMFW_ADSP2_XM, dsp->fw_id);
 	xmalg = dsp->ops->sys_config_size / sizeof(__be32);
 
 	addr = alg_region->base + xmalg + ALG_XM_FIELD(magic);