net/irda: sh_sir: Modify iounmap wrong execution

On sh_sir_probe function, there was a possibility that
iounmap is executed even though self->membase was NULL when error case.
This patch modify it.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: David S. Miller <davem@davemloft.net>