drm/panel: Simplify with dev_err_probe()

dev_err_probe() can check if the error code is -EPROBE_DEFER
and can return the error code, replacing dev_err() with it
simplifies the code.

Signed-off-by: Chen Haonan <chen.haonan2@zte.com.cn>
Reviewed-by: Jessica Zhang <quic_jesszhan@quicinc.com>
Link: https://lore.kernel.org/r/3ac20d355b0b3ad3cedb87c8f4efa819a055624b.1702967834.git.chen.haonan2@zte.com.cn
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/3ac20d355b0b3ad3cedb87c8f4efa819a055624b.1702967834.git.chen.haonan2@zte.com.cn