Drop the vblank reference only after we've done the hideous
need_vlv_dsi_wa stuff. This will make it easier to reuse the
the vblank evasion machinery elsewhere.

Keeping the vblank reference for a bit longer is not a
problem. In fact we might want to not drop it at all until
intel_pipe_update_end(), but we'll leave that idea for later.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231213102519.13500-3-ville.syrjala@linux.intel.comReviewed-by: Uma Shankar <uma.shankar@intel.com>