regmap: cache: Silence checkpatch warning

checkpatch.pl warned:
WARNING: ENOSYS means 'invalid syscall nr' and nothing else
Align the return value to regcache_drop_region().

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Link: https://lore.kernel.org/r/20230313071812.13577-2-alexander.stein@ew.tq-group.com


Signed-off-by: Mark Brown <broonie@kernel.org>