drm/i915: Replace some loop through encoders with intel_pipe_has_type()

In the ironlake mode set code, there was two instances of a loop through
encoders to find out if one of them has INTEL_OUTPUT_LVDS type. Simplify
the code by deleting some lines and use intel_pipe_has_type() instead.

Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>