greybus: loopback: fix connection cleanup paths

The error paths in gb_loopback_connection_init() are kind of screwed
up--not in proper order, and the label naming convention seems a
little inconsistent.

Fix this, ensuring each error cleans up the setup that's been done
up to that point.  Use the convention that the label indicates the
first thing that needs to be cleaned up.

Reorder the statements in gb_loopback_connection_exit() to match
the order of cleanup in gb_loopback_connection_init().

Signed-off-by: Alex Elder <elder@linaro.org>
Reviewed-by: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>