libata-acpi: add missing inlines in libata.h

Adds inline for ata_acpi_unregister/ata_acpi_bind/ata_acpi_unbind
in drivers/ata/libata.h for !CONFIG_ATA_ACPI to fix below warnings.

warning: 'ata_acpi_unregister' defined but not used [-Wunused-function]
warning: 'ata_acpi_bind' defined but not used [-Wunused-function]
warning: 'ata_acpi_unbind' defined but not used [-Wunused-function]
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Lin Ming <ming.m.lin@intel.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

drivers/ata/libata.h

@@ -131,9 +131,9 @@ static inline void ata_acpi_on_disable(struct ata_device *dev) { }
 static inline void ata_acpi_set_state(struct ata_port *ap,
 				      pm_message_t state) { }
 static inline int ata_acpi_register(void) { return 0; }
-static void ata_acpi_unregister(void) { }
-static void ata_acpi_bind(struct ata_device *dev) { }
-static void ata_acpi_unbind(struct ata_device *dev) { }
+static inline void ata_acpi_unregister(void) { }
+static inline void ata_acpi_bind(struct ata_device *dev) { }
+static inline void ata_acpi_unbind(struct ata_device *dev) { }
 #endif
 
 /* libata-scsi.c */