LU-4660 osd-ldiskfs: fix osd_bufs_get() error handling

LU-4660 osd-ldiskfs: fix osd_bufs_get() error handling

Unlock pages just locked during cleanup if page loading failed.

Clean up code style, add function comment blocks.

Signed-off-by: Andriy Skulysh <Andriy_Skulysh@xyratex.com>
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: Ie523b0cfea30bc55ecd58db0849b1b005a393fc7
Reviewed-on: http://review.whamcloud.com/9344
Tested-by: Jenkins
Reviewed-by: Bobi Jam <bobijam@gmail.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>