libxslt: update SRC_URI

libxslt: update SRC_URI

| ERROR: Function failed: Fetcher failure for URL: 'ftp://xmlsoft.org/libxslt/libxslt-1.1.28.tar.gz'. URL ftp://xmlsoft.org/libxslt/libxslt-1.1.28.tar.gz doesn't work
ERROR: Logfile of failure stored in: /home/akuster/oss/maint/poky/build/tmp/work/x86_64-linux/libxslt-native/1.1.28-r0/temp/log.do_checkuri.16102
Log data follows:
| DEBUG: Executing python function do_checkuri
| DEBUG: Testing URL ftp://xmlsoft.org/libxslt/libxslt-1.1.28.tar.gz
| DEBUG: checkstatus() urlopen failed: <urlopen error ftp error: [Errno 110] Connection timed out>
| DEBUG: Python function do_checkuri finished
| ERROR: Function failed: Fetcher failure for URL: 'ftp://xmlsoft.org/libxslt/libxslt-1.1.28.tar.gz'. URL ftp://xmlsoft.org/libxslt/libxslt-1.1.28.tar.gz doesn't work

Signed-off-by: Armin Kuster <akuster808@gmail.com>