Fix compile errors use spandsp with a specific commit

ubuntu/resources/switch/source-release.sh

@@ -56,6 +56,8 @@ make install
 cd /usr/src
 git clone https://github.com/freeswitch/spandsp.git spandsp
 cd spandsp
+git reset --hard 0d2e6ac65e0e8f53d652665a743015a88bf048d4
+/usr/bin/sed -i 's/AC_PREREQ(\[2\.71\])/AC_PREREQ([2.69])/g' /usr/src/spandsp/configure.ac
 sh autogen.sh
 ./configure
 make