USB: Fix cp2101 USB serial device driver termios functions for console use

This is really a follow up to the modifications Alan Cox made for commit
95da310e

 to pass a tty_struct to various
interface functions, which broke the serial configuration (termios) functions
when the device is being used as a console. These changes restore the
configuration to proper functioning both as a tty and as a console.  As Alan
notes in that commit, these changes will need to be tweaked when we have
a proper console abstraction.

Signed-off-by: David VomLehn <dvomlehn@cisco.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>