clk: renesas: rzg2l: Wait for status bit of SD mux before continuing

The hardware user manual for RZ/G2L (r01uh0914ej0130-rzg2l-rzg2lc.pdf,
chapter 7.4.7 Procedure for Switching Clocks by the Dynamic Switching
Frequency Selectors) specifies that we need to check CPG_PL2SDHI_DSEL
for SD clock switching status.

Fixes: eaff3364

 ("clk: renesas: rzg2l: Add SDHI clk mux support")
Signed-off-by: Claudiu Beznea <claudiu.beznea.uj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20230929053915.1530607-3-claudiu.beznea@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>