ARM: dts: stm32: relax qspi pins slew-rate for stm32mp157

Relax qspi pins slew-rate to minimize peak currents.

Fixes: 8440300 ("ARM: dts: stm32: add flash nor support on stm32mp157c eval board")

Link: https://lore.kernel.org/r/20191025130122.11407-1-alexandre.torgue@st.com
Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>
Signed-off-by: Olof Johansson <olof@lixom.net>

arch/arm/boot/dts/stm32mp157-pinctrl.dtsi

@@ -609,13 +609,13 @@
 						 <STM32_PINMUX('F', 6, AF9)>; /* QSPI_BK1_IO3 */
 					bias-disable;
 					drive-push-pull;
-					slew-rate = <3>;
+					slew-rate = <1>;
 				};
 				pins2 {
 					pinmux = <STM32_PINMUX('B', 6, AF10)>; /* QSPI_BK1_NCS */
 					bias-pull-up;
 					drive-push-pull;
-					slew-rate = <3>;
+					slew-rate = <1>;
 				};
 			};
 
@@ -637,13 +637,13 @@
 						 <STM32_PINMUX('G', 7, AF11)>; /* QSPI_BK2_IO3 */
 					bias-disable;
 					drive-push-pull;
-					slew-rate = <3>;
+					slew-rate = <1>;
 				};
 				pins2 {
 					pinmux = <STM32_PINMUX('C', 0, AF10)>; /* QSPI_BK2_NCS */
 					bias-pull-up;
 					drive-push-pull;
-					slew-rate = <3>;
+					slew-rate = <1>;
 				};
 			};