USB: f_mass_storage: fix crash on bind() error

init_completion() hasn't been called yet and the thread isn't created
if we end up here, so don't call complete() on thread_notifier.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
Acked-by: Michal Nazarewicz <m.nazarewicz@samsung.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>