basevideocodec: Reset should reset current caps

basevideocodec: Reset should reset current caps

New caps will need to be negotiated when reset happens
(PAUSED to READY). Without reseting the internal
stored format, basevideoencoder/decoder wouldn't call the
configuration function when the same caps was negotiated
again as they would believe this was the same caps as before.

The issue is that _stop has been called when going to READY and
the elements would have reset their internal codec libs/state as
well. A new configuration should be done.