clk: renesas: rzg2l: Use FIELD_GET() for PLL register fields

clk: renesas: rzg2l: Use FIELD_GET() for PLL register fields

Use FIELD_GET() for PLL register fields.  This is its purpose.

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/20230912045157.177966-14-claudiu.beznea.uj@bp.renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>