drm/i915: Unconfuse pipe vs. crtc->index in i915_get_crtc_scanoutpos()

The "pipe" argument passed in by the vblank code is in fact the crtc
index. Don't assume that is the same as the pipe.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190821173033.24123-2-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>