google/patches/tpu-direct: Finish making .invalidate_mapping optional

This commit:
https://lore.kernel.org/all/20260131-dmabuf-revoke-v7-5-463d956bd527@nvidia.com/
was backported for tpu-direct support. However, I backported the version
of the commit that was present in the mainline kernel: 575157b1b5fc
("dma-buf: Make .invalidate_mapping() truly optional"), which omitted
one ops->invalidate_mappings removal.

Apparently, invalidate_mappings can be NULL during DOCA workloads,
resulting in an -EINVAL return value, causing the workload to fail. Fix
this by removing the check, as was done in the mailing list patch.

BUG=b/563445830
TEST=presubmit, create a3-ultragpu-8g instance and run the repro script
from https://paste.googleplex.com/5626640135225344
RELEASE_NOTE=Fixed a bug which could cause DOCA workloads to fail to initialize.

Signed-off-by: Kevin Berry <kpberry@google.com>
Change-Id: I62a5ae2e9ba6d30632116743aa9c80d84775cce8
Reviewed-on: https://cos-review.googlesource.com/c/third_party/kernel/+/208926
Tested-by: Cusky Presubmit Bot <presubmit@cos-infra-prod.iam.gserviceaccount.com>
Reviewed-by: Anthony Han <anthonyhan@google.com>
Reviewed-by: He Gao <hegao@google.com>