net: ax25: fix misuse of %x

Pointers should be printed with %p or %px rather than
cast to long type and printed with %8.8lx.
Change %8.8lx to %p to print the pointer.

Signed-off-by: Fuqian Huang <huangfq.daxian@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>