eCryptfs: release mutex on hash error path

Release the crypt_stat hash mutex on allocation error. Check for error
conditions when doing crypto hash calls.

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