regmap: Correct comparison in regmap_cached

The cache pointer points to the actual memory used by the cache, as the
comparison here is looking for the type of the cache it should check
against cache_type.

Fixes: 1ea975cf ("regmap: Add a function to check if a regmap register is cached")
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>