fs/ocfs2/dlm: Use GFP_ATOMIC under spin_lock

coccinelle check scripts/coccinelle/locks/call_kern.cocci found that
in fs/ocfs2/dlm/dlmdomain.c an allocation with GFP_KERNEL is done
with locks held:

dlm_query_region_handler
  spin_lock(dlm_domain_lock)
    dlm_match_regions
      kmalloc(GFP_KERNEL)

Change it to GFP_ATOMIC.

Signed-off-by: David Sterba <dsterba@suse.cz>
CC: Joel Becker <joel.becker@oracle.com>
CC: Mark Fasheh <mfasheh@suse.com>
CC: ocfs2-devel@oss.oracle.com

--
Exists in v2.6.37-rc1 and current linux-next.
Signed-off-by: Joel Becker <joel.becker@oracle.com>