ARM: shmobile: r8a7779 dtsi: Remove superfluous interrupt-parent

ARM: shmobile: r8a7779 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" properties in
the serial nodes 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>
(cherry picked from commit 6a7147f53f29887e627d84c0a562c8bb87691e9d)
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>