firmware: cs_dsp: Avoid using a u32 as a __be32 in cs_dsp_mock_mem_maps.c

firmware: cs_dsp: Avoid using a u32 as a __be32 in cs_dsp_mock_mem_maps.c

In cs_dsp_mock_xm_header_drop_from_regmap_cache() for the ADSP2 case read
the big-endian firmware word into a dedicated __be32 variable instead of
using the same u32 for both the big-endian and cpu-endian value.

Fixes: 41e78c0f44f9 ("firmware: cs_dsp: Add mock DSP memory map for KUnit testing")
Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Link: https://patch.msgid.link/20241217113127.186736-1-rf@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>