mf_detect: incorrectly used DTMF_GSIZE instead of MF_GSIZE

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Merged revisions 371662 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 371663 from http://svn.asterisk.org/svn/asterisk/branches/10
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Merged revisions 371664 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@371665 65c4cc65-6c06-0410-ace0-fbb531ad65f3