app_confbridge: Fix confbridge.conf dsp_talking_threshold option setting wrong parameter.

Fixed copy pasta error.

ASTERISK-23545 #close
Reported by: John Knott
........

Merged revisions 411944 from http://svn.asterisk.org/svn/asterisk/branches/11
........

Merged revisions 411945 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@411946 65c4cc65-6c06-0410-ace0-fbb531ad65f3