drm/i915: wait_event_timeout's timeout is in jiffies

So use msecs_to_jiffies(10) to make the timeout the same as in the
"!has_aux_irq" case.

This patch was initially written by Daniel Vetter and posted on
pastebin a few weeks ago. I'm just bringing it to the mailing list.

Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>