fix grain_worker_count max value

[aireenmei]

Description

When len(data_files) < dataloading_host_count, the old way of calculating min_files_per_host gives 0, making the check on line 195 always raise for any grain_worker_count > 0. The right upper bound is files_per_host

Tests

NA

Checklist

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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