drm/panel: Fix a possible null-pointer dereference in jdi_panel_dsi_remove()

In the Linux kernel, the following vulnerability has been resolved:

drm/panel: Fix a possible null-pointer dereference in jdi_panel_dsi_remove()

In jdi_panel_dsi_remove(), jdi is explicitly checked, indicating that it

may be NULL:

if (!jdi)

mipi_dsi_detach(dsi);

However, when jdi is NULL, the function does not return and continues by

calling jdi_panel_disable():

err = jdi_panel_disable(&jdi->base);

Inside jdi_panel_disable(), jdi is dereferenced unconditionally, which can

lead to a NULL-pointer dereference:

struct jdi_panel *jdi = to_panel_jdi(panel);

backlight_disable(jdi->backlight);

To prevent such a potential NULL-pointer dereference, return early from

jdi_panel_dsi_remove() when jdi is NULL.