devfs_unregister_blkdev -- Optionally unregister a conventional block driver.
(unsigned int major, const char * name);
The major number for the driver.
The name of the driver (as seen in /proc/devices).
This function will unregister a block driver provided the "devfs=only"
option was not provided at boot time.
Returns 0 on success, else a negative error code on failure.