iommu/tegra-smmu: Drop unnecessary error check for for debugfs_create_dir()

iommu/tegra-smmu: Drop unnecessary error check for for debugfs_create_dir()

The debugfs_create_dir() function returns error pointers.
It never returns NULL.

As Baolu suggested, this patch removes the error checking for
debugfs_create_dir in tegra-smmu.c. This is because the DebugFS kernel API
is developed in a way that the caller can safely ignore the errors that
occur during the creation of DebugFS nodes. The debugfs APIs have
a IS_ERR() judge in start_creating() which can handle it gracefully. So
these checks are unnecessary.

Fixes: d1313e7896e9 ("iommu/tegra-smmu: Add debugfs support")
Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Suggested-by: Baolu Lu <baolu.lu@linux.intel.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20230901073056.1364755-1-ruanjinjie@huawei.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>