* device with index 'open_device_index' and returns the correspondent
* am7xxx_device in the 'dev' parameter; the function returns 0 on success,
* 1 if the device was already open and a negative value on error.
* device with index 'open_device_index' and returns the correspondent
* am7xxx_device in the 'dev' parameter; the function returns 0 on success,
* 1 if the device was already open and a negative value on error.