drm/panel: remove return value of function drm_panel_add which always return true.

[Bernard]

Hi:

The function "int drm_panel_add(struct drm_panel *panel)" always returns true, this return value is meaningless.
So I am planning to optimize this function to a non-return implementation, "void drm_panel_add(struct drm_panel *panel)".

In order to achieve this optimization, I need to submit a patch series: 
First, modify the code of each submodule that depends on the return value of this function;
And last, replace the declaration in the drm_panel.h file and implementation in the drm_panel.c file;

Do you mind this optimization?
Looking forward to your reply and suggestions!

BR//Bernard