libata: acpi: Remove ata_dev_acpi_handle stub in libata.h

The ata_dev_acpi_handle is defined in libata-acpi.c and the only
external user is libata-zpodd.c, which is built when CONFIG_ATA_ACPI
is set, so there is no need to make an empty stub function for
ONFIG_ATA_ACPI case in libata.h. It also causes compile errors due to
acpi_handle is not defined when !CONFIG_ACPI. This patch fixes this
problem by removing the empty stub.
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Aaron Lu <aaron.lu@intel.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

drivers/ata/libata.h

@@ -133,7 +133,6 @@ static inline void ata_acpi_set_state(struct ata_port *ap,
 				      pm_message_t state) { }
 static inline void ata_acpi_bind_port(struct ata_port *ap) {}
 static inline void ata_acpi_bind_dev(struct ata_device *dev) {}
-static inline acpi_handle ata_dev_acpi_handle(struct ata_device *dev) { return NULL; }
 static inline void ata_scsi_acpi_bind(struct ata_device *dev) {}
 static inline void ata_scsi_acpi_unbind(struct ata_device *dev) {}
 #endif