ocfs2: fix inode leak

We weren't cleaning up our inode reference on error in
ocfs2_reserve_local_alloc_bits(). Add a check for error return and iput() if
need be. Move the code to set the alloc context inode info to the end of the
function so we don't have any possibility of passing back a bad pointer.

Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>