fs/direct-io.c: remove some left over checks

We know that "ret > 0" is true here.  These tests were left over from
commit 02afc27f

 ('direct-io: Handle O_(D)SYNC AIO') and aren't
needed any more.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>