drm/amdgpu: drm_device to amdgpu_device by inline-f (v2)

Get the amdgpu_device from the DRM device by use
of an inline function, drm_to_adev(). The inline
function resolves a pointer to struct drm_device
to a pointer to struct amdgpu_device.

v2: Use a typed visible static inline function
    instead of an invisible macro.

Signed-off-by: Luben Tuikov <luben.tuikov@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
diff --git a/drivers/gpu/drm/amd/amdgpu/df_v3_6.c b/drivers/gpu/drm/amd/amdgpu/df_v3_6.c
index 0aa1ac1..2eab808 100644
--- a/drivers/gpu/drm/amd/amdgpu/df_v3_6.c
+++ b/drivers/gpu/drm/amd/amdgpu/df_v3_6.c
@@ -251,7 +251,7 @@ static ssize_t df_v3_6_get_df_cntr_avail(struct device *dev,
 	int i, count;
 
 	ddev = dev_get_drvdata(dev);
-	adev = ddev->dev_private;
+	adev = drm_to_adev(ddev);
 	count = 0;
 
 	for (i = 0; i < DF_V3_6_MAX_COUNTERS; i++) {