usb: pl2303: do not round to the next nearest standard baud rate for the divisor...

In opposition to the direct baud rate encoding method, the divisor
based method is not limited to a fixed set of standard baud rates.
Hence, there is no need to round to the next nearest standard value.

Reported-by: Mastro Gippo <gipmad@gmail.com>
Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: Reinhard Max <max@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>