staging: most: cdev: fix chrdev_region leak in mod_exit

It looks like v4.18-rc1 commit [0] which upstreams mld-1.8.0
commit [1] missed to fix the memory leak in mod_exit function.

Do it now.

[0] aba258b7 ("staging: most: cdev: fix chrdev_region leak")
[1] https://github.com/microchip-ais/linux/commit/a2d8f7ae7ea381


    ("staging: most: cdev: fix leak for chrdev_region")

Signed-off-by: Suresh Udipi <sudipi@jp.adit-jv.com>
Signed-off-by: Eugeniu Rosca <erosca@de.adit-jv.com>
Acked-by: Christian Gromm <christian.gromm@microchip.com>
Fixes: aba258b7 ("staging: most: cdev: fix chrdev_region leak")
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>