discover/device-handler: Process queue after device added

In device_handler_discover() we process the unresolved boot options
queue first. However the discover_device in question has not yet been
added to handler->devices so when a parser tries to search for a
matching device it will fail.
The discover_device will be added to the handler if it has not already
in device_handler_discover_context_commit() so move the call to
process_boot_option_queue() after it.

Signed-off-by: Samuel Mendoza-Jonas <sam@mendozajonas.com>