staging: most: register channel device after init of struct members

This patch moves the call to device_register to the end of the channel
initialization section that the devcie belongs to. It is needed to
avoid NULL pointer dereferences once the device is registered with
sysfs.

Signed-off-by: Christian Gromm <christian.gromm@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>