drm/i915: simplify config->pixel_multiplier handling

We only ever check whether it's strictly bigger than one, so all the
is_sdvo/is_hdmi checks are redundant. Flatten the code a bit.

Also, s/temp/dpll_md/

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>