ASoC: wm_adsp: Make cirrus_dir const

The cirrus_dir pointer should be const data but was missing the second
const needed to achieve this.

I haven't marked this as a 'Fixes' because it isn't causing any bugs,
it's only a code improvement.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Link: https://patch.msgid.link/20250522103816.543919-1-rf@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: rfvirgil

sound/soc/codecs/wm_adsp.c

@@ -775,7 +775,7 @@ static int wm_adsp_request_firmware_file(struct wm_adsp *dsp,
 	return ret;
 }
 
-static const char *cirrus_dir = "cirrus/";
+static const char * const cirrus_dir = "cirrus/";
 static int wm_adsp_request_firmware_files(struct wm_adsp *dsp,
 					  const struct firmware **wmfw_firmware,
 					  char **wmfw_filename,