Fix MMC numbering issue for Raspberry Pi 3

Using mmc.dtbo from rpi-firmware to switch the controller for the SD
card slot from sdhci to sdhost causes the numbering to change; the
SD card is then not recognized at boot.  Add to the range checked.

Signed-off-by: Matthias Brugger <mbrugger@suse.com>
diff --git a/include/configs/rpi.h b/include/configs/rpi.h
index 55768a4..4c5c1ac 100644
--- a/include/configs/rpi.h
+++ b/include/configs/rpi.h
@@ -137,7 +137,8 @@
 #if CONFIG_IS_ENABLED(CMD_MMC)
 	#define BOOT_TARGET_MMC(func) \
 		func(MMC, mmc, 0) \
-		func(MMC, mmc, 1)
+		func(MMC, mmc, 1) \
+		func(MMC, mmc, 2)
 #else
 	#define BOOT_TARGET_MMC(func)
 #endif