power_supply: Don't use flush_scheduled_work()

flush_scheduled_work() is deprecated and scheduled to be removed.

In battery drivers, the work can be canceled on probe failure and
removal and should be flushed on suspend.  Replace
flush_scheduled_work() usages with direct cancels and flushes.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Anton Vorontsov <cbouatmailru@gmail.com>