Add error checking on initializing registers and interrupt handler.

Initializing registers - lp8727_init_device()
: check i2c error during probing the driver.

Initializing interrupt handler - lp8727_intr_config()
: check an error on creating the irq thread.

If an error occurs on probing lp8727 driver, allocated lp8727 driver memory is freed.
Signed-off-by: Milo(Woogyom) Kim <milo.kim@ti.com>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>