ARM: shmobile: r8a73a4: don't use named irq for DMAEngine

sh-dma-engine driver doesn't care irq name.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>