ANDROID: GKI: scsi.h: add Android ABI padding to a structure

Try to mitigate potential future driver core api changes by adding a
padding to struct scsi_disk.

Based on a change made to the RHEL/CENTOS 8 kernel.

Bug: 151154716
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I1191c786cb341df43a40fa1a82789759b0f431cf