drivers/net/hamradio: fix warning: format not a string literal and no ...

Impact: Use 'static const char[]' instead of 'static char[]' and while
being at it fix an issue in 'mkiss_init_driver', where in case of an
error the status code was not passed to printk.

Fix this warnings:
  drivers/net/hamradio/6pack.c: In function 'sixpack_init_driver':
  drivers/net/hamradio/6pack.c:802: warning: format not a string literal and no format arguments
  drivers/net/hamradio/bpqether.c: In function 'bpq_init_driver':
  drivers/net/hamradio/bpqether.c:609: warning: format not a string literal and no format arguments
  drivers/net/hamradio/mkiss.c: In function 'mkiss_init_driver':
  drivers/net/hamradio/mkiss.c:988: warning: format not a string literal and no format arguments
  drivers/net/hamradio/mkiss.c:991: warning: format not a string literal and no format arguments
  drivers/net/hamradio/scc.c: In function 'scc_init_driver':
  drivers/net/hamradio/scc.c:2109: warning: format not a string literal and no format arguments
  drivers/net/hamradio/yam.c: In function 'yam_init_driver':
  drivers/net/hamradio/yam.c:1094: warning: format not a string literal and no format arguments

Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Signed-off-by: David S. Miller <davem@davemloft.net>