Application of sizeof() to pointer yields the number of bytes of the
pointer, but it should use the length of buffer in the code.

Fixes: 06c2d9a0 ("firmware: tegra: Reduce stack usage")
Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Lv Ruyi <lv.ruyi@zte.com.cn>
Reviewed-by: Jon Hunter <jonathanh@nvidia.com>
Tested-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>