ata_msense_control_spgt2() can be called even for devices that do not
support CDL when the user requests the ALL_SUB_MPAGES mode sense page,
but for such device, this will cause a NULL pointer dereference as
dev->cdl is NULL. Similarly, we should not return any data if
ata_msense_control_spgt2() is called when the user requested the
CDL_T2A_SUB_MPAGE or CDL_T2B_SUB_MPAGE pages for a device that does not
support CDL.

Avoid this potential NULL pointer dereference by checking if the device
support CDL on entry to ata_msense_control_spgt2() and return 0 if it
does not support CDL.

Reported-by: syzbot+37757dc11ee77ef850bb@syzkaller.appspotmail.com
Tested-by: syzbot+37757dc11ee77ef850bb@syzkaller.appspotmail.com
Fixes: 602bcf21 ("ata: libata: Improve CDL resource management")
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>