There is no direct shortcut. I seldom actually create an adjustment layer, I usually create a solid (ctrl + y) or (cmnd + Y on a PC), name the layer, and then click the adjustment layer option in the timeline. I do this because I'm in the habit of naming each element in my comp as it's created. If I use the new adjustment layer option then I have to go back, select the layer, press ctrl + shift + y and re-name the layer after it's created anyway. All that create an adjustment layer does is create a solid the size of your comp, name it Adjustment Layer 1, and turn on the switch. There's no difference between an adjustment layer and a solid in the project window.
If you're really adventurous you can edit the keyboard shortcuts manually. Somewhere there's a tutorial on that.