USB: mos7720: remove broken get_icount and TIOCMIWAIT

Remove broken get_icount and TIOCMIWAIT support.

The driver has an icount structure but it is never been updated which
makes get_icount rather pointless and causes TIOCMIWAIT to always return
-EIO.

Note that the TIOCMIWAIT implementation has always been broken and would
not work even if icount support was added as it does not wait for the
modem status to change (does not use a work queue at all).

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>