scsi: sd: Do not attempt to configure discard unless LBPME is set

Commit f874d72 ("scsi: sd: Keep the discard mode stable") attempted
to address an issue where one mode of discard operation got configured
prior to the device completing full discovery.  Unfortunately this
change assumed discard was always enabled on the device.

Do not attempt to configure discard unless LBPME is enabled.

Link: https://lore.kernel.org/r/20240817005325.3319384-1-martin.petersen@oracle.com
Fixes: f874d72 ("scsi: sd: Keep the discard mode stable")
Reported-by: Chris Bainbridge <chris.bainbridge@gmail.com>
Tested-by: Chris Bainbridge <chris.bainbridge@gmail.com>
Tested-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Tested-by: John Garry <john.g.garry@oracle.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/scsi/sd.c

@@ -3308,6 +3308,9 @@ static void sd_read_app_tag_own(struct scsi_disk *sdkp, unsigned char *buffer)
 
 static unsigned int sd_discard_mode(struct scsi_disk *sdkp)
 {
+	if (!sdkp->lbpme)
+		return SD_LBP_FULL;
+
 	if (!sdkp->lbpvpd) {
 		/* LBP VPD page not provided */
 		if (sdkp->max_unmap_blocks)