ARM: shmobile: r8a7790 dtsi: Remove superfluous interrupt-parent

There's already an "interrupt-parent = <&gic>;" at the top, which is
inherited by all child nodes, so the "interrupt-parent" property in
the sound node can be removed.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Magnus Damm <damm+renesas@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>