cmd: avoid endless loop in sound play command

A parameter starting with a hyphen leads to an endless loop in the sound
play command.

Leave it to dectoul() to handle the hyphen. It will return 0 for a negative
number.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

cmd/sound.c

@@ -48,12 +48,12 @@ static int do_play(struct cmd_tbl *cmdtp, int flag, int argc,
 	++argv;
 	while (argc || first) {
 		first = false;
-		if (argc && *argv[0] != '-') {
+		if (argc) {
 			msec = dectoul(argv[0], NULL);
 			--argc;
 			++argv;
 		}
-		if (argc && *argv[0] != '-') {
+		if (argc) {
 			freq = dectoul(argv[0], NULL);
 			--argc;
 			++argv;