s6e3hc3: not enable auto mode/early exit when dimming on

There is a flickering when enabling auto mode/early exit in dimming on.
Do not enable auto mode/early exit in this condition.

Bug: 194656170
Signed-off-by: William Tai <williamtai@google.com>
Change-Id: I238a49efe3f30a49f2744664e76cabaca009774d
(cherry picked from commit 4b00b2cb)