On spec driver remove, do not clean-up VIC stuff. The VIC should be cleaned
by the mezzanine driver when it release all its handlers (see patch a628fa3).
Just leave a reminder for driver developer when something goes wrong.

Moreove, we do not need to user sver_irq_exit() any more. If the mezzanine
driver is properly written it will clear all its interrupts, and thanks to
patch a628fa3 we can safely assume that everything was cleared.
Signed-off-by: Federico Vaga <federico.vaga@cern.ch>