ARM: dts: sti: remove clk_ignore_unused from bootargs for stih407-b2120

Remove clk_ignore_unused from bootargs as it's no more needed.

Signed-off-by: Patrice Chotard <[e-mail]>

arch/arm/boot/dts/stih407-b2120.dts

···
 	compatible = "st,stih407-b2120", "st,stih407";
 
 	chosen {
-		bootargs = "clk_ignore_unused";
 		stdout-path = &sbc_serial0;
 	};