drm/i915: Remove checks for cloned config with LVDS in dpll code

LVDS is not cloneable, so the check is unnecessary. Removing it makes
the code neater.

v2: Remove checks from GMCH code too, not only ILK+. (Ville)
Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1458576016-30348-2-git-send-email-ander.conselvan.de.oliveira@intel.com