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.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>