libata: remove superfluous NULL pointer checks

host->ports[] always contain pointers to valid port structures since
a "dummy port" structure is used in case if there is no physical port.

This patch takes care of two entries from Dan's list:

drivers/ata/sata_sil.c +535 sil_interrupt(13) warning: variable derefenced before check 'ap'
drivers/ata/sata_mv.c +2517 mv_unexpected_intr(6) warning: variable derefenced before check 'ap'

and of another needless NULL pointer check in pata_octeon_cf.c.

Reported-by: Dan Carpenter <error27@gmail.com>
Cc: corbet@lwn.net
Cc: eteo@redhat.com
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
diff --git a/drivers/ata/pata_octeon_cf.c b/drivers/ata/pata_octeon_cf.c
index 8d9343a..abdd19f 100644
--- a/drivers/ata/pata_octeon_cf.c
+++ b/drivers/ata/pata_octeon_cf.c
@@ -653,7 +653,8 @@
 
 		ap = host->ports[i];
 		ocd = ap->dev->platform_data;
-		if (!ap || (ap->flags & ATA_FLAG_DISABLED))
+
+		if (ap->flags & ATA_FLAG_DISABLED)
 			continue;
 
 		ocd = ap->dev->platform_data;