ARM: dts: r8a7740: Add missing extal2 to CPG node

The Clock Pulse Generator (CPG) device node lacks the extal2 clock.
This may lead to a failure registering the "r" clock, or to a wrong
parent for the "usb24s" clock, depending on MD_CK2 pin configuration and
boot loader CPG_USBCKCR register configuration.

This went unnoticed, as this does not affect the single upstream board
configuration, which relies on the first clock input only.

Fixes: d9ffd583bf345e2e ("ARM: shmobile: r8a7740: add SoC clocks to DTS")
Signed-off-by: Geert Uytterhoeven <[e-mail]>
Reviewed-by: Ulrich Hecht <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/arm/boot/dts/r8a7740.dtsi

···
 		cpg_clocks: cpg_clocks@e6150000 {
 			compatible = "renesas,r8a7740-cpg-clocks";
 			reg = <0xe6150000 0x10000>;
-			clocks = <&extal1_clk>, <&extalr_clk>;
+			clocks = <&extal1_clk>, <&extal2_clk>, <&extalr_clk>;
 			#clock-cells = <1>;
 			clock-output-names = "system", "pllc0", "pllc1",
 					     "pllc2", "r",