mfd: tps65218: Use devm_regmap_add_irq_chip and clean up error path in probe()

Use devm_regmap_add_irq_chip and clean up error path in probe
and also the remove function.

Reported-by: Christian Hohnstaedt <Christian.Hohnstaedt@wago.com>
Signed-off-by: Keerthy <j-keerthy@ti.com>
Reviewed-by: Sebastian Reichel <sebastian.reichel@collabora.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>