nouveau_acpi: convert acpi_get_handle() to acpi_has_method()

acpi_has_method() is a new ACPI API introduced to check
the existence of an ACPI control method.

It can be used to replace acpi_get_handle() in the case that
1. the calling function doesn't need the ACPI handle of the control method.
and
2. the calling function doesn't care the reason why the method is unavailable.

Convert acpi_get_handle() to acpi_has_method()
in drivers/gpu/drm/nouveau/nouveau_acpi.c in this patch.
Signed-off-by: Zhang Rui <rui.zhang@intel.com>
CC: Ben Skeggs <bskeggs@redhat.com>
CC: Dave Airlie <airlied@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/gpu/drm/nouveau/nouveau_acpi.c

@@ -253,18 +253,15 @@ static struct vga_switcheroo_handler nouveau_dsm_handler = {
 
 static int nouveau_dsm_pci_probe(struct pci_dev *pdev)
 {
-	acpi_handle dhandle, nvidia_handle;
-	acpi_status status;
+	acpi_handle dhandle;
 	int retval = 0;
 
 	dhandle = DEVICE_ACPI_HANDLE(&pdev->dev);
 	if (!dhandle)
 		return false;
 
-	status = acpi_get_handle(dhandle, "_DSM", &nvidia_handle);
-	if (ACPI_FAILURE(status)) {
+	if (!acpi_has_method(dhandle, "_DSM"))
 		return false;
-	}
 
 	if (nouveau_test_dsm(dhandle, nouveau_dsm, NOUVEAU_DSM_POWER))
 		retval |= NOUVEAU_DSM_HAS_MUX;