sd: Fix missing ATO tag check

commit e557990e upstream.

3aec2f41 introduced a merge error where we would end up check for
sdkp instead of sdkp->ATO. Fix this so we register app tag capability
correctly.

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: James Bottomley <JBottomley@Odin.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>