drm: Fix misleading documentation of drm_gem_cma_create()

The backing memory does not necessarily have the writecombine attribute
set, since commit cf8ccbc7 ("drm: Add support for GEM buffers backed
by non-coherent memory").

Fixes: cf8ccbc7 ("drm: Add support for GEM buffers backed by non-coherent memory")
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210601095405.8975-1-paul@crapouillou.net

drivers/gpu/drm/drm_gem_cma_helper.c

@@ -104,8 +104,7 @@ __drm_gem_cma_create(struct drm_device *drm, size_t size, bool private)
  * @size: size of the object to allocate
  *
  * This function creates a CMA GEM object and allocates a contiguous chunk of
- * memory as backing store. The backing memory has the writecombine attribute
- * set.
+ * memory as backing store.
  *
  * Returns:
  * A struct drm_gem_cma_object * on success or an ERR_PTR()-encoded negative