f2fs: return error when accessing insane flie offset

commit adb6dc197187e2a5f5a7bed01e722f46a58676af upstream.

If file offset is insane, we have to return error instead of kernel panic.

Reported-by: Eric Zhang <followme999@163.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
Git-commit: 68842d7d
Git-repo: https://android.googlesource.com/kernel/common.git


Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>