tps6586x RTC IRQ is nested threaded and wired to the tps6586x inerrupt
controller. So, this flag is not required for nested irqs anymore,
since commit 3c646f2c ("genirq: Don't suspend nested_thread irqs
over system suspend") was merged.

Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Cc: Lee Jones <lee.jones@linaro.org>
Cc: Nishanth Menon <nm@ti.com>
Cc: Laxman Dewangan <ldewangan@nvidia.com>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>