usb: gadget: f_serial: Ensure gserial disconnected during unbind

usb: gadget: f_serial: Ensure gserial disconnected during unbind

Some UDCs may return an error during pullup disable as part of the
unbind path for a USB configuration.  This will lead to a scenario
where the disable() callback is skipped, whereas the unbind() still
occurs.  If this happens, the u_serial driver will continue to fail
subsequent binds, due to an already existing entry in the ports array.
Ensure that gserial_disconnect() is called during the f_serial unbind,
so the ports entry is properly cleared.

Signed-off-by: Wesley Cheng <quic_wcheng@quicinc.com>
Link: https://lore.kernel.org/r/20220111064850.24311-1-quic_wcheng@quicinc.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>