GFS2: Set log descriptor type for jdata blocks

This patch sets the log descriptor type according to whether the
journal commit is for (journaled) data or metadata. This was
recently broken when the functions to process data and metadata
log ops were combined.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>