gfs2: Use gfs2_holder_initialized for jindex

Before this patch function init_journal() used a local variable jindex to
keep track of whether it needed to dequeue the jindex holder when errors
were found. It also uselessly set the variable just before returning from
the function. This patch simplifies the code by eliminatinng the local
variable in favor of using function gfs2_holder_initialized.

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