drm/i915: Pass dev_priv to cpt_verify_modeset()

Get rid of the last 'dev' usage in ironlake_crtc_enable() by
passing dev_priv to cpt_verify_modeset().

Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191118164430.27265-8-ville.syrjala@linux.intel.com