aio: drop needless assignment in aio_read()

Commit 84c4e1f8 ("aio: simplify - and fix - fget/fput for io_submit()")
refactored aio_read() and some error cases into early return, which made
some intermediate assignment of the return variable needless.

Drop this needless assignment in aio_read().

No functional change. No change in resulting object code.
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/aio.c

@@ -1553,7 +1553,6 @@ static int aio_read(struct kiocb *req, const struct iocb *iocb,
 	file = req->ki_filp;
 	if (unlikely(!(file->f_mode & FMODE_READ)))
 		return -EBADF;
-	ret = -EINVAL;
 	if (unlikely(!file->f_op->read_iter))
 		return -EINVAL;