drm/amd/amdgpu/sdma_v3_0: Fix incorrect param doc-rot issue

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

 drivers/gpu/drm/amd/amdgpu/sdma_v3_0.c:1651: warning: Function parameter or member 'ib' not described in 'sdma_v3_0_emit_copy_buffer'
 drivers/gpu/drm/amd/amdgpu/sdma_v3_0.c:1651: warning: Excess function parameter 'ring' description in 'sdma_v3_0_emit_copy_buffer'

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-sig@lists.linaro.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/sdma_v3_0.c

@@ -1633,7 +1633,7 @@ static void sdma_v3_0_set_irq_funcs(struct amdgpu_device *adev)
 /**
  * sdma_v3_0_emit_copy_buffer - copy buffer using the sDMA engine
  *
- * @ring: amdgpu_ring structure holding ring information
+ * @ib: indirect buffer to copy to
  * @src_offset: src GPU address
  * @dst_offset: dst GPU address
  * @byte_count: number of bytes to xfer