tao3530: Fix usage of mmc rescan

Currently "bootcmd" does not work as intended but instead prints MMC usage
information and goes directly to "nandboot".

Follow what the commit 669681104daa ("configs: Fix usage of mmc rescan")
does for other boards prior to support for TechNexion TAO3530 SoM was
added.

Signed-off-by: Jarkko Nikula <jarkko.nikula@bitmer.com>
diff --git a/include/configs/tao3530.h b/include/configs/tao3530.h
index c34e785..7a54fe3 100644
--- a/include/configs/tao3530.h
+++ b/include/configs/tao3530.h
@@ -114,7 +114,7 @@
 		"bootm ${loadaddr}\0" \
 
 #define CONFIG_BOOTCOMMAND \
-	"if mmc rescan ${mmcdev}; then " \
+	"mmc dev ${mmcdev}; if mmc rescan; then " \
 		"if run loadbootscript; then " \
 			"run bootscript; " \
 		"else " \