Keanu Reeves went to bat for his old director ... but it wasn't enough to keep Carl Rinsch out of prison after the filmmaker was sentenced in his $11 million Netflix fraud case. Here's the deal ... Keanu personally wrote to the judge asking for leniency for Carl -- who directed Keanu in the 2013 movie "47 Ronin" -- calling Carl an "exceptional artist" while acknowledging Carl has a tendency to self-sabotage. Keanu also praised Carl's unfinished Netflix series at the center of the case as "