iommu/tegra241-cmdqv: Staticize cmdqv_debugfs_dir

iommu/tegra241-cmdqv: Staticize cmdqv_debugfs_dir

Fix a sparse warning.

Fixes: 918eb5c856f6 ("iommu/arm-smmu-v3: Add in-kernel support for NVIDIA Tegra241 (Grace) CMDQV")
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202410172003.bRQEReTc-lkp@intel.com/
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20241021230847.811218-1-nicolinc@nvidia.com
Signed-off-by: Will Deacon <will@kernel.org>