drm/rockchip: analogix_dp: Add missing error check for platform_get_resource()

drm/rockchip: analogix_dp: Add missing error check for platform_get_resource()

Add missing error check for platform_get_resource() return value to
prevent NULL pointer dereference when memory resource is not available.

Fixes: 718b3bb9c0ab ("drm/rockchip: analogix_dp: Expand device data to support multiple edp display")
Cc: stable@vger.kernel.org
Signed-off-by: Chen Ni <nichen@iscas.ac.cn>
Reviewed-by: Dragan Simic <dsimic@manjaro.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patch.msgid.link/20260209033123.1089370-1-nichen@iscas.ac.cn