drm/i915/sdvo: Don't unpack stack garbage

Pass the length returned by intel_sdvo_read_infoframe() to
hdmi_infoframe_unpack() so that we don't try to unpack any
leftover stack garbage.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190409144054.24561-6-ville.syrjala@linux.intel.com


Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>