VLC

The deadline computation was shared between the vout thread function and
DisplayPicture(), both by hacking the return value (VLC_EGENERIC meaning
"wait") and using an output parameter, to handle 3 possible cases:
 - VLC_SUCCESS: do not wait
 - VLC_EGENERIC and deadline set: wait for deadline
 - VLC_EGENERIC and deadline not set: wait but no deadline is known

In case of VLC_EGENERIC, the vout thread function computed the max
between the returned value and 100ms.

Simplify by computing the expected deadline from DisplayPicture()
directly.