Consider \begin{equation} \textrm{log} \left( \prod_{i=1}^n y_i \right) = \sum\limits_{i=1}^{n} \textrm{log}(y_i) \geq \textrm{log}(1) = 0 \end{equation}
As $y_i = 2^{k_i}$ then \begin{equation} \textrm{log}(y_i) = \textrm{log}\left(2^{k_i}\right) = k_i \textrm{log}(2) \end{equation}
Therefore an equivalent linearized constraint is: \begin{equation} \sum\limits_{i=1}^{n} k_i \geq 0 \end{equation}
But as $k_i \in \mathbb{N}$ the constraint is always valid.