Replace assignment of 0 to pointer with NULL assignment.

Link: https://lore.kernel.org/r/20191025135010.GA6191@sauravSigned-off-by: NSaurav Girepunje <saurav.girepunje@gmail.com>
Acked-by: NJack Wang <jinpu.wang@cloud.ionos.com>
Signed-off-by: NMartin K. Petersen <martin.petersen@oracle.com>