staging: most: fix race conditions

This patch fixes race conditions that might emerge from functions
aim_open, aim_close, aim_read, aim_write and aim_disconnect_channel
within module cdev.

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