Fix for having multiple same-model FTDI chips with different serial numbers connected at the same time

If you have multiple same-model FTDI chips with different serial numbers connected and using PyFTDI
at the same time, you get an exception:

serial.serialutil.SerialException: Unable to open USB port ftdi://ftdi:ft232h:FTVO7KZ3/1

This is caused by an underlying USBError - because the first PyFTDI does dev.set_configuration(),
which detaches the device driver, then the second PyFTDI tries to do the same, causing an
exception.

This fix now ignores USBError when trying to dev.set_configuration() while in 
get_device() - this probably means there are more than one of the same
kind of FTDI device connected, and the driver has already been detached.