memory: tegra20: Correct comment to MC_STAT registers writes

The code was changed multiple times and the comment to MC_STAT
registers writes became slightly outdated. The MC_STAT programming
now isn't hardcoded to the "bandwidth" mode, let's clarify this in
the comment.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Link: https://lore.kernel.org/r/20210323210446.24867-1-digetx@gmail.com


Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>