samples: mesh: nrf52: amendment in States restoration implementation

For Genric OnPowerUp equal to 0x02 (Restore):
If a transition was in progress when powered down, the element
restores the target state when powered up. Otherwise the element
restores the state it was in when powered down.

This commit implements above mentioned logic.

Signed-off-by: Vikrant More <vikrant8051@gmail.com>