lowmemorykiller: Modify return values to avoid extra calls

idea is taken here:

https://github.com/zarboz/M7wlv_KK_kernel/commit/bb2b43c8f4f340f285ef074603989540c03ad76e

https://github.com/zarboz/M7wlv_KK_kernel/commit/c63e1cfbb9ddbb96e15d7da2b7dddc735bb9392c