drm/amdgpu: Remove amdgpu_gem_map_attach target_dev documentation

The parameter was removed.

Fixes: a19741e5e5a9 "dma_buf: remove device parameter from attach
                     callback v2"
Reviewed-by: Junwei Zhang <Jerry.Zhang@amd.com>
Signed-off-by: Michel Dänzer <michel.daenzer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -191,7 +191,6 @@ error:
 /**
  * amdgpu_gem_map_attach - &dma_buf_ops.attach implementation
  * @dma_buf: shared DMA buffer
- * @target_dev: target device
  * @attach: DMA-buf attachment
  *
  * Makes sure that the shared DMA buffer can be accessed by the target device.