libata: const-ification bombing run

Enforce access rules where appropriate.

If the compiler is smart enough, this may buy us an optimization or two
as a side effect.
diff --git a/drivers/scsi/sata_promise.c b/drivers/scsi/sata_promise.c
index 9bf8cbd..eee93b0 100644
--- a/drivers/scsi/sata_promise.c
+++ b/drivers/scsi/sata_promise.c
@@ -87,8 +87,8 @@
 static void pdc_pata_phy_reset(struct ata_port *ap);
 static void pdc_sata_phy_reset(struct ata_port *ap);
 static void pdc_qc_prep(struct ata_queued_cmd *qc);
-static void pdc_tf_load_mmio(struct ata_port *ap, struct ata_taskfile *tf);
-static void pdc_exec_command_mmio(struct ata_port *ap, struct ata_taskfile *tf);
+static void pdc_tf_load_mmio(struct ata_port *ap, const struct ata_taskfile *tf);
+static void pdc_exec_command_mmio(struct ata_port *ap, const struct ata_taskfile *tf);
 static void pdc_irq_clear(struct ata_port *ap);
 static int pdc_qc_issue_prot(struct ata_queued_cmd *qc);
 
@@ -113,7 +113,7 @@
 	.ordered_flush		= 1,
 };
 
-static struct ata_port_operations pdc_sata_ops = {
+static const struct ata_port_operations pdc_sata_ops = {
 	.port_disable		= ata_port_disable,
 	.tf_load		= pdc_tf_load_mmio,
 	.tf_read		= ata_tf_read,
@@ -136,7 +136,7 @@
 	.host_stop		= ata_pci_host_stop,
 };
 
-static struct ata_port_operations pdc_pata_ops = {
+static const struct ata_port_operations pdc_pata_ops = {
 	.port_disable		= ata_port_disable,
 	.tf_load		= pdc_tf_load_mmio,
 	.tf_read		= ata_tf_read,
@@ -546,7 +546,7 @@
 	return ata_qc_issue_prot(qc);
 }
 
-static void pdc_tf_load_mmio(struct ata_port *ap, struct ata_taskfile *tf)
+static void pdc_tf_load_mmio(struct ata_port *ap, const struct ata_taskfile *tf)
 {
 	WARN_ON (tf->protocol == ATA_PROT_DMA ||
 		 tf->protocol == ATA_PROT_NODATA);
@@ -554,7 +554,7 @@
 }
 
 
-static void pdc_exec_command_mmio(struct ata_port *ap, struct ata_taskfile *tf)
+static void pdc_exec_command_mmio(struct ata_port *ap, const struct ata_taskfile *tf)
 {
 	WARN_ON (tf->protocol == ATA_PROT_DMA ||
 		 tf->protocol == ATA_PROT_NODATA);