f2fs: avoid the global name 'fault_name'

f2fs: avoid the global name 'fault_name'

Non-prefix global name 'fault_name' will pollute global
namespace, fix it.

Refer to:
https://lists.01.org/pipermail/kbuild-all/2018-June/049660.html

To: Jaegeuk Kim <jaegeuk@kernel.org>
To: Chao Yu <yuchao0@huawei.com>
Cc: linux-f2fs-devel@lists.sourceforge.net
Cc: linux-kernel@vger.kernel.org
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>