arm: ti: Fix regression in distro boot for mmc

When devnum was changed to a local variable in distro_bootcmd we ran
into a problem on TI platforms (confirmed on Beaglebone) as we had been
using 'setenv devnum' there as well and it needs to match the other
usage.

Fixes: 13dd6665ed18 ("distro: not taint environment variables if possible")
[trini: Review other platforms, re-word commit message]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/include/environment/ti/mmc.h b/include/environment/ti/mmc.h
index 785fc15..ef05376 100644
--- a/include/environment/ti/mmc.h
+++ b/include/environment/ti/mmc.h
@@ -56,7 +56,7 @@
 			"bootz; " \
 		"fi;\0" \
 	"mmcboot=mmc dev ${mmcdev}; " \
-		"setenv devnum ${mmcdev}; " \
+		"devnum ${mmcdev}; " \
 		"setenv devtype mmc; " \
 		"if mmc rescan; then " \
 			"echo SD/MMC found on device ${mmcdev};" \