[FIx] Fix the total number of iterations in log is a float number.

[jbwang1997]

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Motivation

The log information of total iterations is float type when using IterBasedTrainLoop.

Related issue: #603

Modification

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Checklist

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2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects, like MMDet or MMCls.
4. The documentation has been modified accordingly, like docstring or example tutorials.

[HAOCHENYE]

Should we make sure the type of runner.max_iter is int?

[jbwang1997]

Hello @HAOCHENYE

I convert max_iters and max_epoches to int type when building Loop.