samples: peripheral: lpuart: Fix uart0 pins in nrf52840dk and nrf21540dk

Wrong pins were used for nrf52840dk and nrf21540 uart0 (console uart).
Due to that debug configuration was not printing anything on that DK.

Signed-off-by: Krzysztof Chruściński <[email protected]>
(cherry picked from commit 4b36823)

Author: nordic-krch

samples/peripheral/lpuart/boards/nrf21540dk_nrf52840.overlay

@@ -19,11 +19,11 @@
 	 * observed on nRF21540 v2.0.0 only (~450 uA more than on v1.0.0).
 	 */
 	group1 {
-		psels = <NRF_PSEL(UART_TX, 0, 20)>,
+		psels = <NRF_PSEL(UART_TX, 0, 6)>,
 			<NRF_PSEL_DISCONNECTED(UART_RTS)>;
 	};
 	group2 {
-		psels = <NRF_PSEL(UART_RX, 0, 22)>,
+		psels = <NRF_PSEL(UART_RX, 0, 8)>,
 			<NRF_PSEL_DISCONNECTED(UART_CTS)>;
 	};
 };

samples/peripheral/lpuart/boards/nrf52840dk_nrf52840.overlay

@@ -23,11 +23,11 @@
 	 * observed on nRF52840 v3.0.0 only (~450 uA more then on v2.1.0).
 	 */
 	group1 {
-		psels = <NRF_PSEL(UART_TX, 0, 20)>,
+		psels = <NRF_PSEL(UART_TX, 0, 6)>,
 			<NRF_PSEL_DISCONNECTED(UART_RTS)>;
 	};
 	group2 {
-		psels = <NRF_PSEL(UART_RX, 0, 22)>,
+		psels = <NRF_PSEL(UART_RX, 0, 8)>,
 			<NRF_PSEL_DISCONNECTED(UART_CTS)>;
 	};
 };