Reword ambiguous documentation in Parcel

- original documentation for Parcel.unmarshall could be understood
  both ways: Parcel written with bytes of data, data written with
  bytes of Parcel

Test: Not applicable
Signed-off-by: danielzhang130 <danielzhang130@gmail.com>
Change-Id: I9afd3ae66ca03f391b272ac0524593395ffe53fa
1 file changed