serial: clps711x: Cleanup driver

This patch performs cleanup on clps711x serial driver. This include:
- Change functions naming style.
- Removed unused includes.
- Removed unneeded comments.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>