ASoC: tas2783-sdw: do not treat read-only Controls as writable

The regmap has no writeable_reg callback, so regmap considers every
register up to max_register writable.  That includes the read-only SDCA
Controls the driver itself describes: the Latency of every Entity, the
Clock Valid of every Clock Source, the actual power state of the Power
Domain Entity, the protection status, the algorithm ready flag and the
Extension Unit id and version.  Most of them are also listed in
tas2783_reg_default[] with a placeholder of zero, even though a default
for, say, a latency reading is meaningless.

Reading such a Control caches its real value, which no longer matches
the placeholder, so regcache_sync() then tries to write it back.  The
peripheral rejects the transaction with -ENODATA and the sync aborts,
leaving the rest of the cache unrestored.

Add a writeable_reg callback that refuses the read-only Controls and
otherwise keeps the previous behaviour.  Every selector it lists is the
read-only Control of its Entity type in sdca_function.h, and none of the
Controls the driver writes is affected: the requested power state, the
mutes, the Cluster Index, the protection mode, the algorithm enable and
the file download Controls all stay writable.

The list is static because the BIOS on the affected machines describes
no Smart Amp SDCA function, so the driver runs its fallback tables and
sdca_regmap_writeable() is not available to it.  It would be good to
have the list confirmed against the hardware documentation, and to know
whether the read-only Controls belong in tas2783_reg_default[] at all.

Signed-off-by: Andrey Golovko <andrey.golovko@gmail.com>
Link: https://patch.msgid.link/20260814094000.22118-2-andrey.golovko@gmail.com
Signed-off-by: Mark Brown <broonie@kernel.org>

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