GFS2: Release iopen glock in gfs2_create_inode error cases

Some error cases in gfs2_create_inode were not unlocking the iopen
glock, getting the reference count off. This adds the proper unlock.
The error logic in function gfs2_create_inode was also convoluted,
so this patch simplifies it. It also takes care of a bug in
which gfs2_qa_delete() was not called in an error case.

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