drm/i915: Correct the docs for intel_engine_cmd_parser

In 93b71330 ("drm/i915: Revert "drm/i915/gem: Asynchronous
cmdparser""), the parameters to intel_engine_cmd_parser() were altered
without updating the docs, causing Fi.CI.DOCS to start failing.

Fixes: c9d9fdbc

 ("drm/i915: Revert "drm/i915/gem: Asynchronous cmdparser"")
Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210720182108.2761496-1-jason@jlekstrand.net
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
[Added 'Fixes:' tag and corrected the hash for the ancestor]
(cherry picked from commit 15eb083b

)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
[Updated Fixes tag to match fixes branch]