fix cmd_mmc.c, line 136 missing "

Remove warning for missing " at the end of line 136

Signed-off-by: Reinhard Meyer <u-boot@emk-elektronik.de>
diff --git a/common/cmd_mmc.c b/common/cmd_mmc.c
index a6ed6a8..c0b30d8 100644
--- a/common/cmd_mmc.c
+++ b/common/cmd_mmc.c
@@ -133,7 +133,7 @@
 U_BOOT_CMD(
 	mmcinfo, 2, 0, do_mmcinfo,
 	"display MMC info",
-	"<dev num>\n
+	"<dev num>\n"
         "    - device number of the device to dislay info of\n"
 	""
 );