ax25: Add missing dev_put in ax25_setsockopt

ax25_setsockopt SO_BINDTODEVICE is missing a dev_put call in case of
success.  Re-order code to fix this bug.  While at it also reformat two
lines of code to comply with the Linux coding style.

Initial patch by Jarek Poplawski <jarkao2@gmail.com>.

Reported-by: Bernard Pidoux F6BVP <f6bvp@free.fr>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: David S. Miller <davem@davemloft.net>