The mipi_dsi_dcs_nop() function returns an error but we weren't
checking it in ili9882t_prepare(). Add a check. This is highly
unlikely to matter in practice. If the NOP failed then likely later
MIPI commands would fail too.

Found by code inspection.

Fixes: e2450d32 ("drm/panel: ili9882t: Break out as separate driver")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20240517143643.5.I323476ba9fa8cc7a5adee4c1ec95202785cc5686@changeidSigned-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240517143643.5.I323476ba9fa8cc7a5adee4c1ec95202785cc5686@changeid