apalis-tk1: disable external clock loopback on SDMMC3

Actually make use of that shiny new CONFIG_TEGRA124_MMC_DISABLE_EXT_LOOPBACK.

Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Marcel Ziswiler <marcel@ziswiler.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>
diff --git a/configs/apalis-tk1_defconfig b/configs/apalis-tk1_defconfig
index 7264aee..10862e5 100644
--- a/configs/apalis-tk1_defconfig
+++ b/configs/apalis-tk1_defconfig
@@ -28,6 +28,7 @@
 CONFIG_DFU_MMC=y
 CONFIG_DFU_RAM=y
 # CONFIG_DM_MMC_OPS is not set
+CONFIG_TEGRA124_MMC_DISABLE_EXT_LOOPBACK=y
 CONFIG_E1000=y
 CONFIG_PCI=y
 CONFIG_DM_PCI=y