mms152_ts: bug fixes

- removed autodetecting of max frequency due to a rare exception
- also fixed needless delayed work when long-press-off is set to always on
- manually release all fingers upon screen off to fix a possible bug where
  the touchscreen becomes unresponsive
- manually enable touchscreen on screen-on to fix a possible bug where the
  touchscreen becomes unresponsive because touchwake didn't enable it