accel/amdxdna: Declare npu6_dev_priv as static

Fix sparse warning:
  symbol 'npu6_dev_priv' was not declared. Should it be static?

Fixes: 273b5176 ("accel/amdxdna: Add RyzenAI-npu6 support")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202412311819.9mz11Uak-lkp@intel.com/


Signed-off-by: Lizhi Hou <lizhi.hou@amd.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250102212244.1586340-7-lizhi.hou@amd.com