drm/xe/ads: Use flexible-array

Zero-length arrays are deprecated and flexible arrays should be
used instead: https://www.kernel.org/doc/html/v6.9-rc7/process/deprecated.html#zero-length-and-one-element-arrays

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Julia Lawall <julia.lawall@inria.fr>
Closes: https://lore.kernel.org/r/202405051824.AmjAI5Pg-lkp@intel.com/
Fixes: dd08ebf ("drm/xe: Introduce a new DRM driver for Intel GPUs")
Cc: Matthew Brost <matthew.brost@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240506141917.205714-1-lucas.demarchi@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>

drivers/gpu/drm/xe/xe_guc_ads.c

@@ -109,7 +109,7 @@ struct __guc_ads_blob {
 	struct guc_engine_usage engine_usage;
 	struct guc_um_init_params um_init_params;
 	/* From here on, location is dynamic! Refer to above diagram. */
-	struct guc_mmio_reg regset[0];
+	struct guc_mmio_reg regset[];
 } __packed;
 
 #define ads_blob_read(ads_, field_) \