firmware: cs_dsp: Fix endianness conversion in cs_dsp_mock_wmfw.c

firmware: cs_dsp: Fix endianness conversion in cs_dsp_mock_wmfw.c

In cs_dsp_mock_wmfw_add_coeff_desc() the value stored in longstring->len
needs a cpu_to_le16() conversion.

Fixes: 5cf1b7b47180 ("firmware: cs_dsp: Add mock wmfw file generator for KUnit testing")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202412170233.8DnsdtY6-lkp@intel.com/
Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Link: https://patch.msgid.link/20241217105624.139479-1-rf@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>