configs/engicam_imx6ul_isiot: fix use of incorrect uboot defconfig file

In u-boot v2018.03 release, configs/imx6ul_isiot_mmc_defconfig was
removed and afterwards both emmc and mmc use the same
imx6ul_isiot_emmc_defconfig file so fix the same.

Signed-off-by: Shyam Saini <shyam.saini@amarulasolutions.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

configs/engicam_imx6ul_isiot_defconfig

@@ -15,7 +15,7 @@ BR2_TARGET_UBOOT=y
 BR2_TARGET_UBOOT_BUILD_SYSTEM_KCONFIG=y
 BR2_TARGET_UBOOT_CUSTOM_VERSION=y
 BR2_TARGET_UBOOT_CUSTOM_VERSION_VALUE="2017.07-rc1"
-BR2_TARGET_UBOOT_BOARD_DEFCONFIG="imx6ul_isiot_mmc"
+BR2_TARGET_UBOOT_BOARD_DEFCONFIG="imx6ul_isiot_emmc"
 BR2_TARGET_UBOOT_NEEDS_DTC=y
 BR2_TARGET_UBOOT_NEEDS_OPENSSL=y
 BR2_TARGET_UBOOT_FORMAT_DTB_IMG=y