cmd_mmc: fix arg parsing for setdsr subcmd

The handler do_setdsr receives only the dsr parameter,
the action is parsed before.

Error was introduced when restructuring the mmc command
implementation in commit 1fd93c6e.

Reported-by: Michael Krummsdorf <Michael.Krummsdorf@tq-group.com>
Signed-off-by: Markus Niebel <Markus.Niebel@tq-group.com>

cmd/mmc.c

@@ -710,7 +710,7 @@ static int do_mmc_setdsr(cmd_tbl_t *cmdtp, int flag,
 
 	if (argc != 2)
 		return CMD_RET_USAGE;
-	val = simple_strtoul(argv[2], NULL, 16);
+	val = simple_strtoul(argv[1], NULL, 16);
 
 	mmc = find_mmc_device(curr_device);
 	if (!mmc) {