Remove duplicated code.

aio_aqueue() calls aio_init_aioinfo() as the first action. There is no
need to duplicate the code in kern_aio_fsync().

Also fix indent for aio_aqueue() definition.

Reviewed by: jhb
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D7523