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>
1 file changed