arm: dts: mt7988-sd-rfb: add SD pin driving settings

Set SD pin driving to 4mA

diff --git a/arch/arm/dts/mt7988-sd-rfb.dts b/arch/arm/dts/mt7988-sd-rfb.dts
index a3df37d..9aa198b 100644
--- a/arch/arm/dts/mt7988-sd-rfb.dts
+++ b/arch/arm/dts/mt7988-sd-rfb.dts
@@ -87,10 +87,12 @@
 			pins = "SPI2_CSB", "SPI2_MISO", "SPI2_MOSI",
 			       "SPI2_CLK", "SPI2_HOLD";
 			input-enable;
+			drive-strength = <MTK_DRIVE_4mA>;
 		};
 
 		conf-clk {
 			pins = "SPI2_WP";
+			drive-strength = <MTK_DRIVE_4mA>;
 		};
 	};
 };