Phanbell: Always use MMC0 with Fastboot

* Otherwise, during an SD card boot fastboot will attempt to flash the
SD card. This doesn't work as the partition table is different.
* Also enables a better story for recovering the eMMC - any SD card with
u-boot can use fastboot to reflash.

Change-Id: I0ee135696b55a3e168b0a3aece1d49b736ea81ff
diff --git a/board/freescale/imx8mq_phanbell/imx8mq_phanbell.c b/board/freescale/imx8mq_phanbell/imx8mq_phanbell.c
index d6818bd..5a9f877 100644
--- a/board/freescale/imx8mq_phanbell/imx8mq_phanbell.c
+++ b/board/freescale/imx8mq_phanbell/imx8mq_phanbell.c
@@ -242,7 +242,12 @@
 
 int board_mmc_get_env_dev(int devno)
 {
-	return devno;
+	/*
+	 * This is used for determining which MMC fastboot will flash.
+	 * For Phanbell, we should always flash the eMMC even if booting
+	 * SD. This way SD can be used for recovery.
+	 */
+	return CONFIG_SYS_MMC_ENV_DEV;
 }
 
 int board_late_init(void)