lp8727_charger: Remove unnecessary workqueue thread

LP8727 has two IRQ threads. One is the I2C HW IRQ pin, the other is for
delayed interrupt processing. But this delayed processing can be handled
without additional single thread by using schedule_delayed_work() with
jiffies time value.

Signed-off-by: Milo(Woogyom) Kim <milo.kim@ti.com>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>