drm/amdgpu: Make amdgpu_atif_handler static

There are no external users of function amdgpu_atif_handler so it can
be static.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c

@@ -289,7 +289,7 @@ out:
  * handles it.
  * Returns NOTIFY code
  */
-int amdgpu_atif_handler(struct amdgpu_device *adev,
+static int amdgpu_atif_handler(struct amdgpu_device *adev,
 			struct acpi_bus_event *event)
 {
 	struct amdgpu_atif *atif = &adev->atif;