Update CALLINGSUBADDR channel variable documentation.

(closes issue #15734)
Reported by: alecdavis
Patches:
      channelvariables.tex.diff.txt uploaded by alecdavis (license 585)
Tested by: alecdavis

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@226377 65c4cc65-6c06-0410-ace0-fbb531ad65f3

doc/channelvariables.txt

@@ -701,7 +701,7 @@ ${CALLTYPE}		* Type of call (Speech, Digital, etc)
 ${CALLEDTON}		* Type of number for incoming PRI extension
 			i.e. 0=unknown, 1=international, 2=domestic, 3=net_specific, 
 			4=subscriber, 6=abbreviated, 7=reserved 
-${CALLINGSUBADDR}	* Called PRI Subaddress
+${CALLINGSUBADDR}	* Caller's PRI Subaddress
 ${FAXEXTEN}	 	* The extension called before being redirected to "fax"	
 ${PRIREDIRECTREASON}	* Reason for redirect, if a call was directed
 ${SMDI_VM_TYPE}		* When an call is received with an SMDI message, the 'type'