[MIOpen] Fix -Werror unused parameter 'problem' in InitInvokerFactoryNCHW (ROCm#8206) (ROCm#8214)

## Summary

Fixes ROCm#8206 — build failure on gfx900, gfx906, and
gfx101X-dgpu targets introduced by commit `261cdb8e007` (PR ROCm#7257,
Enable -Werror).

**Root cause:** `InitInvokerFactoryNCHW()` in
`src/ck_impl/implicitgemm_ck_util.hpp` has all its uses of `problem`
inside a `#if MIOPEN_BACKEND_HIP && MIOPEN_USE_COMPOSABLEKERNEL` guard.
The `#else` block already suppressed `ctx`, `kernel_id`, `input1_op`,
`input2_op`, and `output_op` with `(void)` casts — but `problem` was
missed, triggering:

```
implicitgemm_ck_util.hpp:883:77: error: unused parameter 'problem' [-Werror,-Wunused-parameter]
```

**Fix:** Add `(void)problem;` in the existing `#else` block, matching
the pattern used throughout this file (lines 265-268, 393-395, 529-532,
586-590).

**Change:** 1 line added.

## Affected platforms

- Linux: gfx900, gfx906, gfx1010/gfx1011/gfx1012 (gfx101X-dgpu)
- Windows: gfx900, gfx906, gfx101X-dgpu

## Validation plan

- [ ] Local build `--no-ck` (forces `MIOPEN_USE_COMPOSABLEKERNEL=OFF`,
exercises the else branch)
- [ ] Local build default (CK enabled, no regression)
- [ ] TheRock CI with labels `gfx900-linux`, `gfx906-linux`,
`gfx101x-linux` (and Windows variants)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Sonnet 4 <noreply@anthropic.com>

Author: BradPepersAMD

projects/miopen/src/ck_impl/implicitgemm_ck_util.hpp

@@ -1053,6 +1053,7 @@ ConvSolution InitInvokerFactoryNCHW(const ExecutionContext& ctx,
     };
 #else
     (void)ctx;
+    (void)problem;
     (void)kernel_id;
     (void)input1_op;
     (void)input2_op;