ASoC: cs35l56-shared-test: Subtract reg_base offset in dummy regmap

ASoC: cs35l56-shared-test: Subtract reg_base offset in dummy regmap

Subtract the value of cs35l56 regmap_config->reg_base from addresses
passed into the mock regmap bus.

Chip register addresses transferred over SoundWire are offset by 0x8000
to move them after the address range reserved in the SoundWire spec.

This commit prepares for changing the cs35l56-sdw driver to use
regmap_config->reg_base to add this offset. When that is done the
addresses passed into the mock regmap_bus will include this offset.

Signed-off-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Link: https://patch.msgid.link/20260519135435.479949-2-rf@opensource.cirrus.com
Signed-off-by: Mark Brown <broonie@kernel.org>