You don't need to make a seperate sitemap for your blogspot blog. After that you
verify blog, you'll see a link 'Add' in front of your blog's link in the Dashboard of your GWT below the 'sitemap', Click it.
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Click on dropdown-box and choose "Add General Web SiteMap".
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Write "rss.xml" without commas and submit it.
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That's all for sitemap submission of blogspot blog to Google Webmasters tools.