drivers/net/wireless/b43: fix warning: format not a string literal and no ...

Fix this compilation warning:
  drivers/net/wireless/b43/main.c: In function 'b43_print_fw_helptext':
  drivers/net/wireless/b43/main.c:1971: warning: format not a string literal and no format arguments
  drivers/net/wireless/b43/main.c:1973: 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>