ARM: dts: r8a7778: Fix W=1 dtc warnings

Warning (unit_address_vs_reg): Node /sound@ffd90000/rcar_sound,src/src@3 has a unit name, but no reg property
Warning (unit_address_vs_reg): Node /sound@ffd90000/rcar_sound,src/src@4 has a unit name, but no reg property
Warning (unit_address_vs_reg): Node /sound@ffd90000/rcar_sound,src/src@5 has a unit name, but no reg property
Warning (unit_address_vs_reg): Node /sound@ffd90000/rcar_sound,src/src@6 has a unit name, but no reg property
Warning (unit_address_vs_reg): Node /sound@ffd90000/rcar_sound,src/src@7 has a unit name, but no reg property
Warning (unit_address_vs_reg): Node /sound@ffd90000/rcar_sound,src/src@8 has a unit name, but no reg property
Warning (unit_address_vs_reg): Node /sound@ffd90000/rcar_sound,src/src@9 has a unit name, but no reg property
Warning (unit_address_vs_reg): Node /sound@ffd90000/rcar_sound,ssi/ssi@3 has a unit name, but no reg property
Warning (unit_address_vs_reg): Node /sound@ffd90000/rcar_sound,ssi/ssi@4 has a unit name, but no reg property
Warning (unit_address_vs_reg): Node /sound@ffd90000/rcar_sound,ssi/ssi@5 has a unit name, but no reg property
Warning (unit_address_vs_reg): Node /sound@ffd90000/rcar_sound,ssi/ssi@6 has a unit name, but no reg property
Warning (unit_address_vs_reg): Node /sound@ffd90000/rcar_sound,ssi/ssi@7 has a unit name, but no reg property
Warning (unit_address_vs_reg): Node /sound@ffd90000/rcar_sound,ssi/ssi@8 has a unit name, but no reg property
Warning (unit_address_vs_reg): Node /sound@ffd90000/rcar_sound,ssi/ssi@9 has a unit name, but no reg property

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>