drm/fb-cma-helpers: Fix include issue

Exported functions prototypes are missing in drm_fb_cma_helper.c
Include drm_fb_cma_helper to fix that issue.
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@st.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20191119105753.32363-1-benjamin.gaignard@st.com

drivers/gpu/drm/drm_fb_cma_helper.c

@@ -9,6 +9,7 @@
  *  Copyright (C) 2012 Red Hat
  */
 
+#include <drm/drm_fb_cma_helper.h>
 #include <drm/drm_fourcc.h>
 #include <drm/drm_framebuffer.h>
 #include <drm/drm_gem_cma_helper.h>

include/drm/drm_fb_cma_helper.h

@@ -2,6 +2,8 @@
 #ifndef __DRM_FB_CMA_HELPER_H__
 #define __DRM_FB_CMA_HELPER_H__
 
+#include <linux/types.h>
+
 struct drm_framebuffer;
 struct drm_plane_state;