[PATCH] ecryptfs: handle AOP_TRUNCATED_PAGE better

- In fact we don't have to fail if AOP_TRUNCATED_PAGE was returned from
  prepare_write or commit_write. It is beter to retry attempt where it
  is possible.

- Rearange ecryptfs_get_lower_page() error handling logic, make it more clean.

Signed-off-by: Dmitriy Monakhov <dmonakhov@openvz.org>
Acked-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>