firmware: cs_dsp: Fix OOB memory read access in KUnit test (wmfw info)

firmware: cs_dsp: Fix OOB memory read access in KUnit test (wmfw info)

KASAN reported out of bounds access - cs_dsp_mock_wmfw_add_info(),
because the source string length was rounded up to the allocation size.

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/20250523155814.1256762-1-perex@perex.cz
Signed-off-by: Mark Brown <broonie@kernel.org>