i2c-eg20t: Fix flag setting issue

Currently, in case occurring abnormal event,
internal flag variable(=pch_event_flag) is not reset.
This patch fixes the issue.

Signed-off-by: Tomoya MORINAGA <tomoya-linux@dsn.lapis-semi.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>