Revert "drm: Add directive to format code in comment"

Commit 6cc44e9618f03f ("drm: Add directive to format code in comment")
fixes original Sphinx indentation warning as introduced in
471920ce25d50b ("drm/gpuvm: Add locking helpers"), by means of using
code-block:: directive. It semantically conflicts with earlier
bb324f85f72284 ("drm/gpuvm: Wrap drm_gpuvm_sm_map_exec_lock() expected
usage in literal code block") that did the same using double colon
syntax instead. These duplicated literal code block directives causes
the original warnings not being fixed.

Revert 6cc44e9618f03f to keep things rolling without these warnings.

Fixes: 6cc44e9618f0 ("drm: Add directive to format code in comment")
Fixes: 471920ce25d5 ("drm/gpuvm: Add locking helpers")
Signed-off-by: Bagas Sanjaya <[e-mail]>
Reviewed-by: Randy Dunlap <[e-mail]>
Tested-by: Randy Dunlap <[e-mail]>
Signed-off-by: Danilo Krummrich <[e-mail]>

drivers/gpu/drm/drm_gpuvm.c

···
  *
  * The expected usage is:
  *
- * .. code-block:: c
- *
  *    vm_bind {
  *        struct drm_exec exec;
  *