[OpenCL:Chore] Update shared_gather_buf md5 after kernel fix in #4659

[Qxinyu]

Summary

• Follow-up to [OpenCL:Bugfix] Fix maskless attention setArg overflow causing wrong SD UNet output on Adreno (#4653) #4659: the shared_gather_buf.cl fix updated the embedded kernel source (shared_gather_buf_mnn_cl.cpp) but not its entry in OpenCLProgramMd5Map (opencl_source_map.hpp), because opencl_codegen.py writes that header to the script's CWD rather than the cl/ directory.
• The md5 is used to invalidate stale tuning caches when kernel source changes; this syncs it to the fixed kernel (74b2cbe8... → 7bfae0b1..., verified by re-running the codegen — the only real md5 change in the regenerated map).

Test plan

• Re-ran opencl_codegen.py from the cl/ directory and confirmed shared_gather_buf is the only md5 that differs; all other diffs are brace-formatting noise (reverted).

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