eCryptfs: remove unnecessary variable initializations

Andrew Morton wrote:
> >       struct mutex *tfm_mutex = NULL;
>
> This initialisation looks like it's here to kill bogus gcc warning
> (if it is, it should have been commented).  Please investigate
> uninitialized_var() and __maybe_unused sometime.

Remove some unnecessary variable initializations. There may be a few
more such intializations remaining in the code base; a future patch
will take care of those.

Signed-off-by: Michael Halcrow <mhalcrow@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>