ARM: shmobile: r8a7790: add reg-names for sound

Rensas R-Car sound driver supports reg-names.
Let's use it.
Signed-off-by: NKuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: NSimon Horman <horms+renesas@verge.net.au>

arch/arm/boot/dts/r8a7790.dtsi

@@ -1461,6 +1461,8 @@
 			<0 0xec5a0000 0 0x100>,  /* ADG */
 			<0 0xec540000 0 0x1000>, /* SSIU */
 			<0 0xec541000 0 0x1280>; /* SSI */
+		reg-names = "scu", "adg", "ssiu", "ssi";
+
 		clocks = <&mstp10_clks R8A7790_CLK_SSI_ALL>,
 			<&mstp10_clks R8A7790_CLK_SSI9>, <&mstp10_clks R8A7790_CLK_SSI8>,
 			<&mstp10_clks R8A7790_CLK_SSI7>, <&mstp10_clks R8A7790_CLK_SSI6>,