drm/amd/amdgpu/si_dma: Fix some function name disparity

Fixes the following W=1 kernel build warning(s):

drivers/gpu/drm/amd/amdgpu/si_dma.c:320: warning: expecting prototype for cik_dma_vm_copy_pte(). Prototype was for si_dma_vm_copy_pte() instead
drivers/gpu/drm/amd/amdgpu/si_dma.c:412: warning: expecting prototype for si_dma_pad_ib(). Prototype was for si_dma_ring_pad_ib() instead
drivers/gpu/drm/amd/amdgpu/si_dma.c:425: warning: expecting prototype for cik_sdma_ring_emit_pipeline_sync(). Prototype was for si_dma_ring_emit_pipeline_sync() instead

Cc: Alex Deucher <[e-mail]>
Cc: "Christian König" <[e-mail]>
Cc: David Airlie <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: Sumit Semwal <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Cc: [e-mail]
Signed-off-by: Lee Jones <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

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

···
 }
 
 /**
- * cik_dma_vm_copy_pte - update PTEs by copying them from the GART
+ * si_dma_vm_copy_pte - update PTEs by copying them from the GART
  *
  * @ib: indirect buffer to fill with commands
  * @pe: addr of the page entry
···
 }
 
 /**
- * si_dma_pad_ib - pad the IB to the required number of dw
+ * si_dma_ring_pad_ib - pad the IB to the required number of dw
  *
  * @ring: amdgpu_ring pointer
  * @ib: indirect buffer to fill with padding
···
 }
 
 /**
- * cik_sdma_ring_emit_pipeline_sync - sync the pipeline
+ * si_dma_ring_emit_pipeline_sync - sync the pipeline
  *
  * @ring: amdgpu_ring pointer
  *