arm: ti: Add missing "=" from previous fix

While the original patch to fix a regression in distro boot for mmc on
these platforms had the correct syntax, I broke the change while
applying.  Add back in the missing "=" here so that the syntax is
correct.

Reported-by: Andre Heider <a.heider@gmail.com>
Fixes: 27e0f3bcf075 ("arm: ti: Fix regression in distro boot for mmc")
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/include/environment/ti/mmc.h b/include/environment/ti/mmc.h
index ef05376..bb4af0a 100644
--- a/include/environment/ti/mmc.h
+++ b/include/environment/ti/mmc.h
@@ -56,7 +56,7 @@
 			"bootz; " \
 		"fi;\0" \
 	"mmcboot=mmc dev ${mmcdev}; " \
-		"devnum ${mmcdev}; " \
+		"devnum=${mmcdev}; " \
 		"setenv devtype mmc; " \
 		"if mmc rescan; then " \
 			"echo SD/MMC found on device ${mmcdev};" \