arm64: dts: renesas: r8a7795: add missing dma-names on hscif2

hscif2 has 4 dmas, but has only 2 dma-names.
This patch add missing dma-names.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Fixes: e0f0bda7 ("arm64: dts: renesas: r8a7795: sort subnodes
of the soc node")
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>