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

In the Linux kernel, the following vulnerability has been resolved: 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.