V4L/DVB (7830): dvb_ca_en50221: Fix High CPU load in 'top' due to budget_av slot polling

This change addresses kernel bug #10459: In kernel 2.6.25 the
budget_av driver polls for an CI slot in 100ms intervals (because no
interrupt solution for budget_av cards is feasible due to HW reasons).
If no CI/CAM is connected to the DVB card, polling times out only after 250ms.
This periodic polling leads to high CPU load.

The change increases the polling interval for empty slots from 100ms to 5s.
Intervals for remaining slot states (invalid, in progress, ready) are unchanged,
as they are either temporary conditions or no timeout should occur.

Signed-off-by: Robert Schedel <r.schedel@yahoo.de>
Signed-off-by: Oliver Endriss <o.endriss@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>