clk: renesas: r8a7745: Remove PLL configs for MD19=0

According to tables 7.5b and 7.6b of the RZ/G Series Hardware User's
Manual Rev.1.00, MD19=0 is a prohibited setting.

Hence stop looking at MD19, and remove all PLL configurations for
MD19=0.

Fixes: 9127d54b ("clk: renesas: cpg-mssr: Add R8A7745 support")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>