drm/atomic: Remove unneeded null check for private objects

It can be seen in drm_atomic_get_private_obj_state() that
ptr will never be NULL, so skip the check for that case.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170927083532.5756-1-maarten.lankhorst@linux.intel.comReviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/drm_atomic.c

@@ -182,9 +182,6 @@ void drm_atomic_state_default_clear(struct drm_atomic_state *state)
 	for (i = 0; i < state->num_private_objs; i++) {
 		struct drm_private_obj *obj = state->private_objs[i].ptr;
 
-		if (!obj)
-			continue;
-
 		obj->funcs->atomic_destroy_state(obj,
 						 state->private_objs[i].state);
 		state->private_objs[i].ptr = NULL;

include/drm/drm_atomic.h

@@ -768,8 +768,7 @@ void drm_state_dump(struct drm_device *dev, struct drm_printer *p);
 		     ((obj) = (__state)->private_objs[__i].ptr, \
 		      (old_obj_state) = (__state)->private_objs[__i].old_state,	\
 		      (new_obj_state) = (__state)->private_objs[__i].new_state, 1); \
-	     (__i)++) \
-		for_each_if (obj)
+	     (__i)++)
 
 /**
  * for_each_old_private_obj_in_state - iterate over all private objects in an atomic update
@@ -787,8 +786,7 @@ void drm_state_dump(struct drm_device *dev, struct drm_printer *p);
 	     (__i) < (__state)->num_private_objs && \
 		     ((obj) = (__state)->private_objs[__i].ptr, \
 		      (old_obj_state) = (__state)->private_objs[__i].old_state, 1); \
-	     (__i)++) \
-		for_each_if (obj)
+	     (__i)++)
 
 /**
  * for_each_new_private_obj_in_state - iterate over all private objects in an atomic update
@@ -806,8 +804,7 @@ void drm_state_dump(struct drm_device *dev, struct drm_printer *p);
 	     (__i) < (__state)->num_private_objs && \
 		     ((obj) = (__state)->private_objs[__i].ptr, \
 		      (new_obj_state) = (__state)->private_objs[__i].new_state, 1); \
-	     (__i)++) \
-		for_each_if (obj)
+	     (__i)++)
 
 /**
  * drm_atomic_crtc_needs_modeset - compute combined modeset need