regmap: Clarify error for unknown cache types

The error message printed when we fail to locate the cache type the map
requested says it can't find a compress type rather than a cache type,
fix that. Since the compressed type is the only one currently compiled
conditionally it's likely to be the missing type but that might not always
be true and is still unclear.

Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20230324-regcache-unknown-v1-1-80deecbf196b@kernel.org