staging: most: aim-cdev: report error returned by alloc_chrdev_region

This patch forwards the error code returned by function
alloc_chrdev_region(). It is needed to stop the module
from hiding the actual cause of failure.

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