LU-1337 osc: fix -Werror=unused-result

LU-1337 osc: fix -Werror=unused-result

Newer Fedora kernels build using -Werror=unused-result.  It appears
that GOTO() isn't correctly assigning rc in this instance.  The
unused PTR_ERR() is generating warning which is upgraded to an error.

Signed-off-by: chas williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Change-Id: I66d730d4d0e20f0f1c7671dc00acefdf7ed1fbe9
Reviewed-on: http://review.whamcloud.com/3638
Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Yang Sheng <yang.sheng@intel.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>