mpi: Fix haloupdate with inner dim [v2]

[codecov[bot]]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Comparison is base (7a86b36) 86.80% compared to head (d6d8a6e) 86.82%.

Files	Patch %	Lines
devito/mpi/halo_scheme.py	75.00%	2 Missing :warning:
devito/ir/clusters/algorithms.py	94.73%	0 Missing and 1 partial :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2272 +/- ## ========================================== + Coverage 86.80% 86.82% +0.02% ========================================== Files 229 229 Lines 42296 42383 +87 Branches 7830 7845 +15 ========================================== + Hits 36713 36797 +84 - Misses 4923 4926 +3 Partials 660 660 ```

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