fuse: direct-io: don't dirty ITER_BVEC pages

fuse: direct-io: don't dirty ITER_BVEC pages

When reading from a loop device backed by a fuse file it deadlocks on
lock_page().

This is because the page is already locked by the read() operation done on
the loop device.  In this case we don't want to either lock the page or
dirty it.

So do what fs/direct-io.c does: only dirty the page for ITER_IOVEC vectors.

Orabug : 22652336

Reported-by: Alexey Kodanev <alexey.kodanev@oracle.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Signed-off-by: Ashish Samant <ashish.samant@oracle.com>
Acked-by: Srinivas Eeda <srinivas.eeda@oracle.com>