chan_dahdi/sig_pri: Fix type mismatch in the idledial feature's channel creation.

Square pegs in round holes don't work very well.
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Merged revisions 418261 from http://svn.asterisk.org/svn/asterisk/branches/1.8


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/11@418262 f38db490-d61c-443f-a65b-d21fe96a405b