zephyr: update name of nrf5340 dk

This to correctly set the kconfig default value.

Signed-off-by: Håkon Øye Amundsen <haakon.amundsen@nordicsemi.no>
Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>
diff --git a/boot/zephyr/Kconfig b/boot/zephyr/Kconfig
index 0e00758..0e92566 100644
--- a/boot/zephyr/Kconfig
+++ b/boot/zephyr/Kconfig
@@ -429,7 +429,7 @@
 	default 6 if BOARD_NRF9160DK_NRF9160
 	default 11 if BOARD_NRF52840DK_NRF52840
 	default 13 if BOARD_NRF52DK_NRF52832
-	default 23 if BOARD_NRF5340_DK_NRF5340_CPUAPP || BOARD_NRF5340_DK_NRF5340_CPUAPPNS
+	default 23 if BOARD_NRF5340PDK_NRF5340_CPUAPP || BOARD_NRF5340PDK_NRF5340_CPUAPPNS
 	help
 	  Pin on the serial detect port which triggers serial recovery mode.