drm/amdgpu: Fix memory leak

drm_gem_object_put() should be paired with drm_gem_object_lookup().

All gem objs are saved in fb->base.obj[]. Need put the old first before
assign a new obj.

Trigger VRAM leak by running command below
$ service gdm restart

Signed-off-by: xinhui pan <xinhui.pan@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_display.c

@@ -955,8 +955,9 @@ int amdgpu_display_framebuffer_init(struct drm_device *dev,
 	}
 
 	for (i = 1; i < rfb->base.format->num_planes; ++i) {
+		drm_gem_object_get(rfb->base.obj[0]);
+		drm_gem_object_put(rfb->base.obj[i]);
 		rfb->base.obj[i] = rfb->base.obj[0];
-		drm_gem_object_get(rfb->base.obj[i]);
 	}
 
 	return 0;
@@ -1002,6 +1003,7 @@ amdgpu_display_user_framebuffer_create(struct drm_device *dev,
 		return ERR_PTR(ret);
 	}
 
+	drm_gem_object_put(obj);
 	return &amdgpu_fb->base;
 }