dist/common/scripts/scylla_cpuscaling_setup: fix file open mode for writing
dist/common/scripts/scylla_cpuscaling_setup: fix file open mode for writing

gentoo linux part tries to open the configuration file without the
write flag, leading to an exception

Signed-off-by: Alexys Jacob <ee25f2b26a23c85eb2940a5214ecb1801c877d19@gentoo.org>
Message-Id: <20181002123957.6010-1-ee25f2b26a23c85eb2940a5214ecb1801c877d19@gentoo.org>

scylladb/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,avikivity/scylla