devicestate: Make ast_devstate_changed_literal() return value and doxygen consistent.

devicestate: Make ast_devstate_changed_literal() return value and doxygen consistent.

Nothing actually cares about the value anyway.

(closes issue ASTERISK-23178)
Reported by: Jonathan Rose
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Merged revisions 407337 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 407338 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 407339 from http://svn.asterisk.org/svn/asterisk/branches/12

git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@407340 65c4cc65-6c06-0410-ace0-fbb531ad65f3