drm/panel: kingdisplay-kd097d04: Delete panel on attach() failure

If we fail to attach (e.g., because 1 of 2 dual-DSI controllers aren't
ready), we leave a dangling drm_panel reference to freed memory. Clean
that up on failure.

Fixes: 2a994cbe ("drm/panel: Add Kingdisplay KD097D04 panel driver")
Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210923173336.1.Icb4d9dbc1817f4e826361a4f1cea7461541668f0@changeid