ANDROID: dm-crypt: Remove WQ_NON_REENTRANT flag.

Fix the build of drivers/md/dm-crypt.c.

In 82c6fea6 "ANDROID: dm-crypt: run in a WQ_HIGHPRI workqueue"
a change was cherry-picked from an earlier kernel which had
the WQ_NON_REENTRANT flag. As per Documentation/workqueue.txt,
this flag has been removed from the kernel and all WQs are
non-reentrant. It is not appropriate for 3.18.

Signed-off-by: Alistair Strachan <alistair.strachan@imgtec.com>