[CK_TILE] Rename Stream-K grid function
## Motivation
This PR introduces a change in the name of the get_grid function in the
Stream-K TilePartitioner to avoid confusion with a similarly named
method. In the Stream-K TilePartitioner, there is get_grid() which
returns num_cu*occupancy and there is grid_size() which returns the grid
size used to launch the kernel. In this PR, we change get_grid() to be
get_max_active_wgs() to better reflect what the function returns and not
confuse it with grid_size().
## Technical Details
Initially in the Stream-K TilePartitioner we had get_grid() which
returned grid_. We are renaming get_grid() to get_max_active_wgs() and
grid_ to max_active_wgs_ internally, while keeping grid_size() the same.
The parameter, grid, for the Stream-K TilePartitioner remains the same
to maintain consistency with the rest of the Stream-K API.
## Test Plan
Validated using the test suite that is already present.
## Test Result
All tests passed
## Submission Checklist
- [x] Look over the contributing guidelines at
https://github.com/ROCm/ROCm/blob/develop/CONTRIBUTING.md#pull-requests.
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