gpio: tegra: Prefer kcalloc() over kzalloc() with multiplies

Rather than manually compute the size of an array, pass the number and
element size to kcalloc().

Signed-off-by: Thierry Reding <treding@nvidia.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>