Fix building chan_phone on big endian systems

A left over from the formats conversion (Corey Farrell).

AST-24458 #close
Review: https://reviewboard.asterisk.org/r/4117/


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/13@426570 f38db490-d61c-443f-a65b-d21fe96a405b