drm/i915: don't wait for vblank while writing InfoFrames

This function is called when the pipe is disabled, so it always gets
the 50ms timeout.

This function is called once for each InfoFrame, so we actually get a
100ms timeout. Will be more if we add more InfoFrames.

Also, the spec says we need to "wait for a VSync to ensure completion
of any pending DIP transmissions", not for a VBlank. OTOH, the
register documentation suggests that the DIPs are sent *during* the
VSync, so shouldn't we be waiting until *after* the VSync to ensure
all DIPs are sent?

So this wait_for_vblank seems, besides useless, totally wrong.

If we ever want to change some specific InfoFrame on-the-fly (outside
of the modeset code), the code that changes the InfoFrame will have to
do the waiting itself, and properly.

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