drm/i915: Rewrite some some of the FDI lane checks

The logic in the FDI lane checks is very hard for my poor brain to
grasp. Rewrite it in a more straightforward way.

Cc: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_display.c

@@ -5580,14 +5580,13 @@ static bool ironlake_check_fdi_lanes(struct drm_device *dev, enum pipe pipe,
 		}
 		return true;
 	case PIPE_C:
-		if (!pipe_has_enabled_pch(pipe_B_crtc) ||
-		    pipe_B_crtc->config->fdi_lanes <= 2) {
 		if (pipe_config->fdi_lanes > 2) {
-				DRM_DEBUG_KMS("invalid shared fdi lane config on pipe %c: %i lanes\n",
+			DRM_DEBUG_KMS("only 2 lanes on pipe %c: required %i lanes\n",
 				      pipe_name(pipe), pipe_config->fdi_lanes);
 			return false;
 		}
-		} else {
+		if (pipe_has_enabled_pch(pipe_B_crtc) &&
+		    pipe_B_crtc->config->fdi_lanes > 2) {
 			DRM_DEBUG_KMS("fdi link B uses too many lanes to enable link C\n");
 			return false;
 		}