drm/i915: reduce indent in pch detection

Save some horizontal space.

Reviewed-by: David Weinehall <david.weinehall@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180202130416.18233-1-jani.nikula@intel.com