Provided that d is a constant, rather than a CVX variable or expression, you can multiply out the denominator
x <= d*(b-c*x)
Note: I used non-strict inequality. if you use a stric inequality in CVX, it will be treated as non-strict inequality.
if d is a CvX variable or expression, the constraint is non-convex.
And if you want to help yourself, the best way is to follow the advice I provided in reply to your previous question. About division in constraints