at91_ide: turn on PIO 6 support

As we have already PIO 6 transfer mode supported in IDE layer, we can turn
it on in the driver.

Signed-off-by: Stanislaw Gruszka <[e-mail]>
Tested-by: "Steve Wootton" <[e-mail]>
Cc: Sergei Shtylyov <[e-mail]>
Signed-off-by: Bartlomiej Zolnierkiewicz <[e-mail]>

drivers/ide/at91_ide.c

···
 	.tp_ops		= &at91_ide_tp_ops,
 	.host_flags 	= IDE_HFLAG_MMIO | IDE_HFLAG_NO_DMA | IDE_HFLAG_SINGLE |
 			  IDE_HFLAG_NO_IO_32BIT | IDE_HFLAG_UNMASK_IRQS,
-	.pio_mask 	= ATA_PIO5,
+	.pio_mask 	= ATA_PIO6,
 };
 
 /*