LU-7311 osd: ext4_bread has one less parameter in kernel 3.18

LU-7311 osd: ext4_bread has one less parameter in kernel 3.18

The returned error code was the 5th parameter to ext4_bread until the
kernel 3.18. It was then removed and integrated into the returned
pointer. Create a shim to emulate the newer version of ext4_bread with
older kernels.

Signed-off-by: frank zago <fzago@cray.com>
Change-Id: I3dacd8b24ae7a3a823f5cc662b2ee3627f8fcda7
Reviewed-on: http://review.whamcloud.com/16892
Tested-by: Jenkins
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>