soc/tegra: pmc: Use lower-case for hexadecimal literals

The remainder of the file uses lower-case for hexadecimal literals, so
change the only odd-one-out occurrence for consistency.

Signed-off-by: Thierry Reding <treding@nvidia.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>