drm/amd/display: Fix incorrect size calculation for loop

In the Linux kernel, the following vulnerability has been resolved: drm/amd/display: Fix incorrect size calculation for loop [WHY] fe_clk_en has size of 5 but sizeof(fe_clk_en) has byte size 20 which is lager than the array size. [HOW] Divide byte size 20 by its element size. This fixes 2 OVERRUN issues reported by Coverity.