fs/direct-io.c: adjust suspicious bit operation

fs/direct-io.c: adjust suspicious bit operation

READ is 0, so the result of the bit-and operation is 0.  Rewrite with == as
done elsewhere in the same file.

This problem was found using Coccinelle (http://coccinelle.lip6.fr/).

Signed-off-by: Julia Lawall <julia@diku.dk>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>