Commit 95733b3a9 introduced the `StoreGroupID()` function, but that
unfortunately set an empty key in the journal.
Passing the `csiGroupIDKey` key (with value `csi.groupid`) caused
setting `csi.csi.groupid` as a key. Reading the value back with the
right `csi.groupid` key always returned an empty value.
Fixes: 95733b3a9 "journal: add option to store the groupID"
Signed-off-by: Niels de Vos <ndevos@ibm.com>