Replace assignment of 0 to pointer with NULL assignment.

Link: https://lore.kernel.org/r/20191024025726.GA31421@sauravSigned-off-by: Saurav Girepunje <saurav.girepunje@gmail.com>
Acked-by: Dick Kennedy <dick.kennedy@broadcom.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>