firmware: cs_dsp: Fix OOB memory read access in KUnit test (ctl cache)

KASAN reported out of bounds access - cs_dsp_ctl_cache_init_multiple_offsets().
The code uses mock_coeff_template.length_bytes (4 bytes) for register value
allocations. But later, this length is set to 8 bytes which causes
test code failures.

As fix, just remove the lenght override, keeping the original value 4
for all operations.

Cc: Simon Trimmer <simont@opensource.cirrus.com>
Cc: Charles Keepax <ckeepax@opensource.cirrus.com>
Cc: Richard Fitzgerald <rf@opensource.cirrus.com>
Cc: patches@opensource.cirrus.com
Cc: stable@vger.kernel.org
Signed-off-by: Jaroslav Kysela <perex@perex.cz>
Reviewed-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Link: https://patch.msgid.link/20250523154151.1252585-1-perex@perex.cz
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: perexg

drivers/firmware/cirrus/test/cs_dsp_test_control_cache.c

@@ -776,7 +776,6 @@ static void cs_dsp_ctl_cache_init_multiple_offsets(struct kunit *test)
 					      "dummyalg", NULL);
 
 	/* Create controls identical except for offset */
-	def.length_bytes = 8;
 	def.offset_dsp_words = 0;
 	def.shortname = "CtlA";
 	cs_dsp_mock_wmfw_add_coeff_desc(local->wmfw_builder, &def);