ata-acpi: don't call _GTF for disabled drive

I got below log after a S3 resume in a ASUS A6VC laptop. The system has
only one IDE drive. It appears there is no reason calling _GTF for
disabled drive.

ACPI Error (dsopcode-0483): Attempt to CreateField of length zero [20070126]
ACPI Error (psparse-0537): Method parse/execution failed [\_SB_.PCI0.IDE0.RATA] (Node df822a7c), AE_AML_OPERAND_VALUE
ACPI Error (psparse-0537): Method parse/execution failed [\_SB_.PCI0.IDE0.CHN1.DRV0._GTF] (Node df822bd0), AE_AML_OPERAND_VALUE
ata2.00: _GTF evaluation failed (AE 0x3006)
ACPI Error (dsopcode-0483): Attempt to CreateField of length zero [20070126]
ACPI Error (psparse-0537): Method parse/execution failed [\_SB_.PCI0.IDE0.RATA] (Node df822a7c), AE_AML_OPERAND_VALUE
ACPI Error (psparse-0537): Method parse/execution failed [\_SB_.PCI0.IDE0.CHN1.DRV1._GTF] (Node df822b94), AE_AML_OPERAND_VALUE
ata2.01: _GTF evaluation failed (AE 0x3006)
Signed-off-by: NShaohua Li <shaohua.li@intel.com>
Signed-off-by: NJeff Garzik <jgarzik@redhat.com>

drivers/ata/libata-acpi.c

@@ -839,7 +839,8 @@ void ata_acpi_on_resume(struct ata_port *ap)
 		 */
 		ata_link_for_each_dev(dev, &ap->link) {
 			ata_acpi_clear_gtf(dev);
-			if (ata_dev_get_GTF(dev, NULL) >= 0)
+			if (ata_dev_enabled(dev) &&
+			    ata_dev_get_GTF(dev, NULL) >= 0)
 				dev->flags |= ATA_DFLAG_ACPI_PENDING;
 		}
 	} else {
@@ -849,7 +850,8 @@ void ata_acpi_on_resume(struct ata_port *ap)
 		 */
 		ata_link_for_each_dev(dev, &ap->link) {
 			ata_acpi_clear_gtf(dev);
-			dev->flags |= ATA_DFLAG_ACPI_PENDING;
+			if (ata_dev_enabled(dev))
+				dev->flags |= ATA_DFLAG_ACPI_PENDING;
 		}
 	}
 }