net/hamradio/6pack: Fix inconsistent indenting

Eliminate the follow smatch warning:

drivers/net/hamradio/6pack.c:728 sixpack_ioctl() warn: inconsistent
indenting.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Jiapeng Chong <jiapeng.chong@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>