[IRDA]: Missing allocation result check in irlap_change_speed().

The skb allocation may fail, which can result in a NULL pointer dereference
in irlap_queue_xmit().

Coverity CID: 434.

Signed-off-by: Florin Malita <fmalita@gmail.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>