[IRDA]: irda parameters warning fixes.

This patch fixes:
  CHECK   /home/kernel/src/net/irda/parameters.c
/home/kernel/src/net/irda/parameters.c:466:2: warning: Using plain integer as NULL pointer
/home/kernel/src/net/irda/parameters.c:520:2: warning: Using plain integer as NULL pointer
/home/kernel/src/net/irda/parameters.c:573:2: warning: Using plain integer as NULL pointer

Signed-off-by: Richard Knutsson <ricknu-0@student.ltu.se>
Signed-off-by: Samuel Ortiz <samuel@sortiz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>