drm/gpuvm: Fix kernel-doc warning for drm_gpuvm_map_req.map

The kernel-doc for struct drm_gpuvm_map_req.map was added as '@op_map'
instead of '@map', leading to this warning during htmldocs build:

WARNING: include/drm/drm_gpuvm.h:1083 struct member 'map' not described in 'drm_gpuvm_map_req'

Fixes: 000a45dce7ad ("drm/gpuvm: Pass map arguments through a struct")
Reported-by: Stephen Rothwell <[e-mail]>
Closes: https://lore.kernel.org/all/[e-mail]/
Signed-off-by: Ankan Biswas <[e-mail]>
Signed-off-by: Danilo Krummrich <[e-mail]>

include/drm/drm_gpuvm.h

···
  */
 struct drm_gpuvm_map_req {
 	/**
-	 * @op_map: struct drm_gpuva_op_map
+	 * @map: struct drm_gpuva_op_map
 	 */
 	struct drm_gpuva_op_map map;
 };