greybus: module: fix double freeing of module structure

The module will be released by gb_module_release() once all references
for the module are dropped. And so there is no need to free it in the
error path specially.

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