libata: fix error checking in in ata_parse_force_one()

ata_parse_force_one() was incorrectly comparing @p to @endp when it
should have been comparing @id.  The only consequence is that it may
end up using an invalid port number in "libata.force" module param
instead of rejecting it.
Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-by: Petru-Florin Mihancea <petrum@gmail.com>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=195785

drivers/ata/libata-core.c

@@ -6800,7 +6800,7 @@ static int __init ata_parse_force_one(char **cur,
 	}
 
 	force_ent->port = simple_strtoul(id, &endp, 10);
-	if (p == endp || *endp != '\0') {
+	if (id == endp || *endp != '\0') {
 		*reason = "invalid port/link";
 		return -EINVAL;
 	}