Fix T85225: Variable scope in ridged multi-fractal noise
This patch fixes a bug introduced in rB74188e65028d268af887ab2140e4253087410c1e. The commit incorrectly moved the declaration and intialization of the variable `pwr` inside the loop. Since the value was originally modified in each iteration based on it's previous value and `pwHL` through `pwr *= pwHL`, this change in scope was wrong. It resetted the value in each iteration. This patch moves the declaration of `pwr` outside the loop again.