serial: sh-sci: use driver core functions, not sysfs ones.

This is a driver, do not call "raw" sysfs functions, instead call driver
core ones.  Specifically convert the use of sysfs_create_file() and
sysfs_remove_file() to use device_create_file() and device_remove_file()

Cc: Jiri Slaby <jslaby@suse.com>
Cc: linux-serial@vger.kernel.org
Link: https://lore.kernel.org/r/20190704084617.3602-4-gregkh@linuxfoundation.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>