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>