[IRDA] irda-usb: use NULL instead of 0

Use NULL instead of 0 for a null pointer value (sparse warning):

drivers/net/irda/irda-usb.c:1781:30: warning: Using plain integer as NULL pointer

Also, correct timeout argument to use milliseconds instead of jiffies.

Signed-off-by: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: David S. Miller <davem@davemloft.net>