drm/i915: Update docs in intel_wakeref.h

Fix docs for __intel_wakeref_put() and intel_wakeref_get() to
reflect current behaviour.

Signed-off-by: Nirmoy Das <nirmoy.das@intel.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230105203843.30663-1-nirmoy.das@intel.com