Wrong peak times units when upsampling is different than 4 in FlashCamExtractor

[clara-escanuela]

Describe the bug
Peak times are not properly transformed to ns when the upsampling is not set to the default value.

To Reproduce
Look at dl1 peak time images of the FlashCam for different upsamplings.

Expected behavior
Peak times with units of ns.

Additional context
Add any other context about the problem here.