libata: clear PIO pad area

ata_sff_data_xfer[32]() use pad area if the transfer size isn't
multiple of transfer size; however, this area wasn't cleared and
garbage data in pad area could be transferred to the device.  Make
sure the pad area is cleared.
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Lei Ming <tom.leiming@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/libata-sff.c

@@ -569,7 +569,7 @@ unsigned int ata_sff_data_xfer(struct ata_device *dev, unsigned char *buf,
 
 	/* Transfer trailing byte, if any. */
 	if (unlikely(buflen & 0x01)) {
-		unsigned char pad[2];
+		unsigned char pad[2] = { };
 
 		/* Point buf to the tail of buffer */
 		buf += buflen - 1;
@@ -628,7 +628,7 @@ unsigned int ata_sff_data_xfer32(struct ata_device *dev, unsigned char *buf,
 
 	/* Transfer trailing bytes, if any */
 	if (unlikely(slop)) {
-		unsigned char pad[4];
+		unsigned char pad[4] = { };
 
 		/* Point buf to the tail of buffer */
 		buf += buflen - slop;