fix cmd_mmc.c, line 136 missing "

Remove warning for missing " at the end of line 136
Signed-off-by: NReinhard Meyer <u-boot@emk-elektronik.de>

common/cmd_mmc.c

@@ -133,7 +133,7 @@ int do_mmcinfo (cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 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"
 	""
 );