mtx: print a usage message when no device is specified

Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
mtx: print usage if there was no valid command specified

Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
mtx: make sure return status is non-zero if the device was not a changer

Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
mtx: fix how we calculate element addresses in the ui

Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Merge pull request #41 from sahlberg/mtx-updates

Mtx updates