greybus: loopback: ensure sysfs entries are cleaned up on exit

bdd4bba4 ('greybus/loopback: add module level sys/debug fs data points')
added a sysfs entry attached to gb_dev but missed the jump to out_sysfs_dev
This patchs fixes the missing jump to out_sysfs_dev.

Signed-off-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Reported-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>