LU-6400 osd: initialize variable before use

LU-6400 osd: initialize variable before use

ldisk_bread use a pointer return error value. But not
initialized it. So maybe return a random value even in
normal case.

Signed-off-by: Yang Sheng <yang.sheng@intel.com>
Change-Id: I2ab424b285003c85b63dbea0b787b606fc368245
Reviewed-on: http://review.whamcloud.com/16008
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>