staging: most: net: hold used net device

This adds the dev_hold and dev_put calls to the functions
aim_resume_tx_channel, aim_rx_data and on_netinfo to postpone the
unregistration of the used net device.

Signed-off-by: Andrey Shvetsov <andrey.shvetsov@k2l.de>
Signed-off-by: Christian Gromm <christian.gromm@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>