aoe: do not call bdi_init after blk_alloc_queue

aoe: do not call bdi_init after blk_alloc_queue

commit 0a41409c518083133e79015092585d68915865be upstream, but doesn't
apply, so this version is different for older kernels than 3.7.x

blk_alloc_queue has already done a bdi_init, so do not bdi_init
again in aoeblk_gdalloc.  The extra call causes list corruption
in the per-CPU backing dev info stats lists.

Affected users see console WARNINGs about list_del corruption on
percpu_counter_destroy when doing "rmmod aoe" or "aoeflush -a"
when AoE targets have been detected and initialized by the
system.

The patch below applies to v3.6.11, with its v47 aoe driver.  It
is expected to apply to all currently maintained stable kernels
except 3.7.y.  A related but different fix has been posted for
3.7.y.

References:

  RedHat bugzilla ticket with original report
  https://bugzilla.redhat.com/show_bug.cgi?id=853064

  LKML discussion of bug and fix
  http://thread.gmane.org/gmane.linux.kernel/1416336/focus=1416497

Reported-by: Josh Boyer <jwboyer@redhat.com>
Signed-off-by: Ed Cashin <ecashin@coraid.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>