USB: cp210x: allow more baud rates above 1Mbaud

Allow more baud rates to be set in [1M,2M] baud.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Cc: Preston Fick <preston.fick@silabs.com>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>