arm: dts: an7581: set r_smpl for MMC in U-Boot

When booting from SPI, the ROM code does not initialize the MMC
controller on AN7581. As a result, the first MMC initialization
is performed by U-Boot.

In this case, the r_smpl bit is left uninitialized, which may
cause incorrect sampling timing during early MMC access.

Set the r_smpl bit explicitly in the U-Boot device tree to ensure
reliable MMC initialization.

This change is limited to the U-Boot-specific device tree.
The Linux MMC driver already performs runtime delay detection
and does not require a fixed r_smpl setting.

Signed-off-by: Ray Liu <ray.xy.liu@gmail.com>

arch/arm/dts/an7581-u-boot.dtsi

@@ -84,6 +84,7 @@
 			reg = <0x0 0x1fa0e000 0x0 0x1000>,
 				<0x0 0x1fa0c000 0x0 0x60>;
 			interrupts = <GIC_SPI 170 IRQ_TYPE_LEVEL_HIGH>;
+			r_smpl = <1>;
 			clocks = <&scuclk EN7581_CLK_EMMC>, <&clk25m>;
 			clock-names = "source", "hclk";
 			bus-width = <4>;