ASoC: mt6358: Remove undefined HPx Mux enumeration values

ASoC: mt6358: Remove undefined HPx Mux enumeration values

The HPx Mux enumerations define values 5, 6 and 7 but describe them as
"undefined" and map them to the value 0 on writing. Given the descriptions
and behaviour it seems that these values are invalid and should not be
present in the register, the current behaviour is detected as problematic
by mixer-test:

# # HPL Mux.0 expected 5 but read 0, is_volatile 0
# # HPL Mux.0 expected 6 but read 0, is_volatile 0
# # HPL Mux.0 expected 7 but read 0, is_volatile 0

Remove the values from the enumeration, this will prevent userspace setting
them.

Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230224-asoc-mt6358-quick-fixes-v1-3-747d9186be4b@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>