drm/i915: Avoid drm_atomic_state_put(NULL) on error paths

The error paths in hsw_trans_edp_pipe_A_crc_wa() and
intel_prepare_reset() would potentially call drm_atomic_state_put with a
NULL state, which would lead to a NULL pointer dereference.

Found by coverity.

v2: Improve the error paths. (Chris)

Fixes: 0853695c3b ("drm: Add reference counting to drm_atomic_state")
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: <drm-intel-fixes@lists.freedesktop.org> # v4.10-rc1+
Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1484742868-9551-1-git-send-email-ander.conselvan.de.oliveira@intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/intel_display.c

@@ -3560,23 +3560,19 @@ void intel_prepare_reset(struct drm_i915_private *dev_priv)
 	state = drm_atomic_helper_duplicate_state(dev, ctx);
 	if (IS_ERR(state)) {
 		ret = PTR_ERR(state);
-		state = NULL;
 		DRM_ERROR("Duplicating state failed with %i\n", ret);
-		goto err;
+		return;
 	}
 
 	ret = drm_atomic_helper_disable_all(dev, ctx);
 	if (ret) {
 		DRM_ERROR("Suspending crtc's failed with %i\n", ret);
-		goto err;
+		drm_atomic_state_put(state);
+		return;
 	}
 
 	dev_priv->modeset_restore_state = state;
 	state->acquire_ctx = ctx;
-	return;
-
-err:
-	drm_atomic_state_put(state);
 }
 
 void intel_finish_reset(struct drm_i915_private *dev_priv)