USB: CP2101 Support AN205 baud rates

This patch adds support for the extended range of baud rates supported
by CP2102 and CP2103 devices described in SiLabs AN205.  An additional
function cp2101_quantise_baudrate rounds the baud rate as per AN205
Table 1.  A modification to the baud rate calculation removes a rounding
error, allowing the full range of baud rates to be used.

Signed-off-by: Craig Shelley <craig@microtron.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>