scripts/dowload.pl: use glob to expand target dir

scripts/dowload.pl: use glob to expand target dir

If CONFIG_DOWNLOAD_FOLDER is set to for example "~/dl", the download
script fails to create the .hash and .dl files with the following
errors:
 Cannot create file ~/dl/dropbear-2017.75.tar.bz2.dl: No such file or directory
 sh: 1: cannot create ~/dl/dropbear-2017.75.tar.bz2.hash: Directory nonexistent

If the tarball already exists in the ~/dl dir, it's properly found and
used, so this issue only affects the download.pl script.
 This patch calls glob() on the target dir parameter, which will expand `~`.

Signed-off-by: Zoltan Gyarmati <mr.zoltan.gyarmati@gmail.com>