ata: libata: ata_{sff|std}_prereset() always return 0

ata_std_prereset() always returns 0, hence the check in ata_sff_prereset()
is pointless and thus it also can return only 0 (however, we cannot change
the prototypes of ata_{sff|std}_prereset() as they implement the driver's
prereset() method).

Found by Linux Verification Center (linuxtesting.org) with the SVACE static
analysis tool.
Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>

drivers/ata/libata-core.c

@@ -3568,7 +3568,7 @@ EXPORT_SYMBOL_GPL(ata_wait_after_reset);
  *	Kernel thread context (may sleep)
  *
  *	RETURNS:
- *	0 on success, -errno otherwise.
+ *	Always 0.
  */
 int ata_std_prereset(struct ata_link *link, unsigned long deadline)
 {

drivers/ata/libata-sff.c

@@ -1708,16 +1708,15 @@ EXPORT_SYMBOL_GPL(ata_sff_thaw);
  *	Kernel thread context (may sleep)
  *
  *	RETURNS:
- *	0 on success, -errno otherwise.
+ *	Always 0.
  */
 int ata_sff_prereset(struct ata_link *link, unsigned long deadline)
 {
 	struct ata_eh_context *ehc = &link->eh_context;
 	int rc;
 
-	rc = ata_std_prereset(link, deadline);
-	if (rc)
-		return rc;
+	/* The standard prereset is best-effort and always returns 0 */
+	ata_std_prereset(link, deadline);
 
 	/* if we're about to do hardreset, nothing more to do */
 	if (ehc->i.action & ATA_EH_HARDRESET)