build_oai: correct doxygen path in logging statement

Correctly show the path: it was missing cmake_targets/, although it is
there.

Closes: #733

cmake_targets/build_oai

@@ -504,7 +504,7 @@ function main() {
     # Doxygen Support #
     ###################
     if [ "$BUILD_DOXYGEN" = "1" ] ; then
-	echo_info "Built Doxygen based documentation. The documentation file is located here: $OPENAIR_DIR/$BUILD_DIR/build/html/index.html"
+	echo_info "Built Doxygen based documentation. The documentation file is located here: $DIR/$BUILD_DIR/build/doc/html/index.html"
     fi
 
     # TODO: once we got the CMakeLists.txt file done for the ORAN files, remove the following lines