drm/i915/gem: reconcile Excess struct member kernel-doc warnings

Document nested struct members with full names as described in
Documentation/doc-guide/kernel-doc.rst.

i915_gem_context_types.h:420: warning: Excess struct member 'lock' description in 'i915_gem_context'
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: intel-gfx@lists.freedesktop.org
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: dri-devel@lists.freedesktop.org
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231226195432.10891-1-rdunlap@infradead.org

drivers/gpu/drm/i915/gem/i915_gem_context_types.h

@@ -412,9 +412,9 @@ struct i915_gem_context {
 
 	/** @stale: tracks stale engines to be destroyed */
 	struct {
-		/** @lock: guards engines */
+		/** @stale.lock: guards engines */
 		spinlock_t lock;
-		/** @engines: list of stale engines */
+		/** @stale.engines: list of stale engines */
 		struct list_head engines;
 	} stale;
 };