drm: remove excess description

Description of expected_size doesn't match any parameter of the function
drm_atomic_replace_property_blob. Removing it.

Signed-off-by: Luis de Bethencourt <[e-mail]>
Signed-off-by: Daniel Vetter <[e-mail]>
Link: http://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/drm_atomic.c

···
  * drm_atomic_replace_property_blob - replace a blob property
  * @blob: a pointer to the member blob to be replaced
  * @new_blob: the new blob to replace with
- * @expected_size: the expected size of the new blob
  * @replaced: whether the blob has been replaced
  *
  * RETURNS: