greybus: connection: Exit connection before destroying it

gb_connection_create() can initialize a connection if bundle->device id
is valid. And so the connection must be destroyed by calling
gb_connection_exit() before gb_connection_destroy(). This wasn't done in
the code that is parsing the manifest.

Fix it.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>