uart: sdm845: Fix debug UART pinmux

Configure debug UART pins as function: "qup9" rather than being regular
gpios. It fixes a hang seen during pinmux setting.

Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
Reviewed-by: Ramon Fried <rfried.dev@gmail.com>
diff --git a/arch/arm/dts/sdm845.dtsi b/arch/arm/dts/sdm845.dtsi
index b9506f1..df5b6df 100644
--- a/arch/arm/dts/sdm845.dtsi
+++ b/arch/arm/dts/sdm845.dtsi
@@ -47,7 +47,7 @@
 			/* DEBUG UART */
 			qup_uart9: qup-uart9-default {
 				pins = "GPIO_4", "GPIO_5";
-				function = "gpio";
+				function = "qup9";
 			};
 		};