soc/tegra: fuse: Clear fuse->clk on driver probe failure

The fuse->clk must be cleared if FUSE driver fails to probe, otherwise
tegra_fuse_readl() will crash. It's unlikely to happen in practice,
nevertheless let's correct it for completeness.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>