drm/prime: Remove duplicate forward declaration

struct device is forward-declared twice. Remove the second instance.
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180111201730.30708-1-thierry.reding@gmail.com

include/drm/drm_prime.h

@@ -61,8 +61,6 @@ struct drm_device;
 struct drm_gem_object;
 struct drm_file;
 
-struct device;
-
 /* core prime functions */
 struct dma_buf *drm_gem_dmabuf_export(struct drm_device *dev,
 				      struct dma_buf_export_info *exp_info);