Hi there,
Thank you for the information. The problem you are experiencing is not because of a white bar, actually, it is because of the dimension of the images that you used in the Revolution Slider. As the image needs to be correct width/height wise and to avoid having the image skewed, the image gets smaller on height when the width of the browser is getting smaller which is the case for mobile view.
I used the Google Chrome Developer Toolbar and shrink the browser window to show you exactly what is happening:
Now the Revolution Slider has a method to fix this issue which you need to follow using this tutorial:
Also, there is a tutorial regarding the overall responsive slide creation which will be a great help:
https://www.themepunch.com/faq/slider-revolution-responsive-tutorial-5-0/
Thank you.