libata-acpi: adjust constness in ata_acpi_gtm/stm() parameters

* No internal function uses const ata_port.  Drop const from @ap.

* Make ata_acpi_stm() copy @stm before using it and change @stm to
  const.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
diff --git a/include/linux/libata.h b/include/linux/libata.h
index ef52a07..1ca9b89 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -940,8 +940,8 @@
 /* libata-acpi.c */
 #ifdef CONFIG_ATA_ACPI
 extern int ata_acpi_cbl_80wire(struct ata_port *ap);
-int ata_acpi_stm(const struct ata_port *ap, struct ata_acpi_gtm *stm);
-int ata_acpi_gtm(const struct ata_port *ap, struct ata_acpi_gtm *stm);
+int ata_acpi_stm(struct ata_port *ap, const struct ata_acpi_gtm *stm);
+int ata_acpi_gtm(struct ata_port *ap, struct ata_acpi_gtm *stm);
 #else
 static inline int ata_acpi_cbl_80wire(struct ata_port *ap) { return 0; }
 #endif