regmap: Modify map->cache_bypass directly

In preperation for the upcoming patches, modify map->cache_bypass
directly.  The helper functions will grab an exclusive lock.  Because
we'll have acquired the same lock we need to avoid a deadlock.

Signed-off-by: Dimitris Papastamos <dp@opensource.wolfsonmicro.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>