clk: renesas: rcar-gen3: Pass name/offset to cpg_sd_clk_register()

Explicitly pass the clock's name and register offset to
cpg_sd_clk_register(), so the latter doesn't have to extract them from
the cpg_core_clk object.

This keeps all cpg_core_clk parsing and unmarshalling contained in a
single function (rcar_gen3_cpg_clk_register()).

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>