NFS: Fix two bugs in the O_DIRECT write code

Do not flag an error if the COMMIT call fails and we decide to resend the
writes. Let the resend flag the error if it fails.

If a write has failed, then nfs_direct_write_result should not attempt to
send a commit. It should just exit asap and return the error to the user.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>