drm/plane: Remove redundant extern

Use of the extern keyword for function prototypes is unnecessary, so it
can be removed.
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

include/drm/drm_plane_helper.h

@@ -43,8 +43,7 @@
  * planes.
  */
 
-extern int drm_crtc_init(struct drm_device *dev,
-			 struct drm_crtc *crtc,
+int drm_crtc_init(struct drm_device *dev, struct drm_crtc *crtc,
 		  const struct drm_crtc_funcs *funcs);
 
 /**
@@ -79,7 +78,7 @@ static inline void drm_plane_helper_add(struct drm_plane *plane,
 	plane->helper_private = funcs;
 }
 
-extern int drm_plane_helper_check_update(struct drm_plane *plane,
+int drm_plane_helper_check_update(struct drm_plane *plane,
 				  struct drm_crtc *crtc,
 				  struct drm_framebuffer *fb,
 				  struct drm_rect *src,
@@ -90,15 +89,15 @@ extern int drm_plane_helper_check_update(struct drm_plane *plane,
 				  bool can_position,
 				  bool can_update_disabled,
 				  bool *visible);
-extern int drm_primary_helper_update(struct drm_plane *plane,
+int drm_primary_helper_update(struct drm_plane *plane,
 			      struct drm_crtc *crtc,
 			      struct drm_framebuffer *fb,
 			      int crtc_x, int crtc_y,
 			      unsigned int crtc_w, unsigned int crtc_h,
 			      uint32_t src_x, uint32_t src_y,
 			      uint32_t src_w, uint32_t src_h);
-extern int drm_primary_helper_disable(struct drm_plane *plane);
-extern void drm_primary_helper_destroy(struct drm_plane *plane);
+int drm_primary_helper_disable(struct drm_plane *plane);
+void drm_primary_helper_destroy(struct drm_plane *plane);
 extern const struct drm_plane_funcs drm_primary_helper_funcs;
 
 int drm_plane_helper_update(struct drm_plane *plane, struct drm_crtc *crtc,