Replace errant tabs with spaces in causes.h.

(closes issue ASTERISK-20826)
Reported by: snuffy
Patches:
	notabs.dif uploaded by snuffy (license 5024)
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Merged revisions 378733 from http://svn.asterisk.org/svn/asterisk/branches/1.8
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Merged revisions 378734 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@378735 65c4cc65-6c06-0410-ace0-fbb531ad65f3