irda: Free skb on irda_accept error path.

skb is not freed if newsk is NULL. Rework the error path so free_skb is
unconditionally called on function exit.

Fixes: c3ea9fa2 ("[IrDA] af_irda: IRDA_ASSERT cleanups")
Signed-off-by: Phil Turnbull <phil.turnbull@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>