up_down_mixer: reject unsupported channel configurations

init_mix() left mix_routine NULL for combos unhandled by
select_mix_out_*() but accepted by set_downmix_coefficients()
add NULL-check before calling set_downmix_coefficients()

Signed-off-by: Adrian Bonislawski <adrian.bonislawski@intel.com>

Author: abonislawski

src/audio/up_down_mixer/up_down_mixer.c

@@ -307,6 +307,12 @@ static int init_mix(struct processing_module *mod,
 		return -EINVAL;
 	}
 
+	/* select_mix_out_*() return NULL for unsupported in/out combos */
+	if (!cd->mix_routine) {
+		comp_err(dev, "unsupported channel configuration");
+		return -EINVAL;
+	}
+
 	/* Update audio format. */
 	cd->out_fmt[0].valid_bit_depth = IPC4_DEPTH_24BIT;
 	cd->out_fmt[0].depth = IPC4_DEPTH_32BIT;