usb: gadget: qdss: Don't clear debug_inface_enabled upon unbind

The debug_inface_enabled flag is used to enable the additional
control interface.  This is usually set by userspace prior to
creating a ConfigFS configuration.  However, currently the flag
is automatically cleared whenever the function is unbound.
This will result in incorrect enumeration if userspace attempts
to rebind the ConfigFS gadget without resetting the flag.

Instead, clear the flag only from qdss_free_func() which is
called when the QDSS instance is removed from the config.  When
it is re-added upon composition switch it is reasonable to
expect that userspace will properly set the flag again if needed.

Change-Id: I3f961b5226c5270f23140c5999d776e83b7e9b15
Signed-off-by: Jack Pham <jackp@codeaurora.org>
Signed-off-by: Krishna Kurapati <quic_kriskura@quicinc.com>