drm/radeon: Prevent multiple debug error lines on suspend

Fix to avoid multiple debug error lines printed on every suspend by Radeon driver's debugfs.

radeon_debugfs_init() calls debugfs_create_file() for every ring.

This results in printing multiple error lines to the screen and dmesg similar to this:

[   92.378726] debugfs: File 'radeon_ring_gfx' in directory '0000:00:01.0' already present!
[   92.378732] debugfs: File 'radeon_ring_cp1' in directory '0000:00:01.0' already present!
[   92.378734] debugfs: File 'radeon_ring_cp2' in directory '0000:00:01.0' already present!
[   92.378737] debugfs: File 'radeon_ring_dma1' in directory '0000:00:01.0' already present!
[   92.378739] debugfs: File 'radeon_ring_dma2' in directory '0000:00:01.0' already present!
[   92.380775] debugfs: File 'radeon_ring_uvd' in directory '0000:00:01.0' already present!
[   92.406620] debugfs: File 'radeon_ring_vce1' in directory '0000:00:01.0' already present!
[   92.406624] debugfs: File 'radeon_ring_vce2' in directory '0000:00:01.0' already present!

Patch v1: The fix was to run lookup() for the file before trying to (re)create that debug file.
Patch v2: Call the radeon_debugfs_init() only once when radeon ring is initialized (as suggested
by Christian K. - thanks)
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Woody Suwalski <terraluna977@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_ring.c

@@ -413,6 +413,7 @@ int radeon_ring_init(struct radeon_device *rdev, struct radeon_ring *ring, unsig
 			dev_err(rdev->dev, "(%d) ring map failed\n", r);
 			return r;
 		}
+		radeon_debugfs_ring_init(rdev, ring);
 	}
 	ring->ptr_mask = (ring->ring_size / 4) - 1;
 	ring->ring_free_dw = ring->ring_size / 4;
@@ -421,7 +422,6 @@ int radeon_ring_init(struct radeon_device *rdev, struct radeon_ring *ring, unsig
 		ring->next_rptr_gpu_addr = rdev->wb.gpu_addr + index;
 		ring->next_rptr_cpu_addr = &rdev->wb.wb[index/4];
 	}
-	radeon_debugfs_ring_init(rdev, ring);
 	radeon_ring_lockup_update(rdev, ring);
 	return 0;
 }