drm/rockchip: analogix_dp: drop unnecessary probe deferral "error" print

This driver is the only user of of_drm_find_panel() which prints an
error before doing probe deferral, yielding messages like this on boot,
before eventually succeeding:

[    2.234271] [drm:rockchip_dp_probe] *ERROR* failed to find panel
...
[    4.797539] [drm:rockchip_dp_probe] *ERROR* failed to find panel
...

Let's just drop the message.

Signed-off-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>