drm/rockchip: dw_dp: Fix null-ptr-deref in dw_dp_remove()

drm/rockchip: dw_dp: Fix null-ptr-deref in dw_dp_remove()

Attempting to access driver data in the platform driver ->remove()
callback may lead to a null pointer dereference since there is no
guaranty that the component ->bind() callback invoking
platform_set_drvdata() was executed.

A common scenario is when Rockchip DRM driver didn't manage to run
component_bind_all() because of an (unrelated) error causing early
return from rockchip_drm_bind().

Drop the unnecessary call to platform_get_drvdata() and, instead,
reference the target device structure via platform_device.

Fixes: d68ba7bac955 ("drm/rockchip: Add RK3588 DPTX output support")
Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patch.msgid.link/20260310-drm-rk-fixes-v2-3-645ecfb43f49@collabora.com