drm/komeda: check for error-valued pointer

komeda_pipeline_get_state() may return an error-valued pointer, thus
check the pointer for negative or null value before dereferencing.

Fixes: 502932a0 ("drm/komeda: Add the initial scaler support for CORE")
Signed-off-by: Amjad Ouled-Ameur <amjad.ouled-ameur@arm.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240610102056.40406-1-amjad.ouled-ameur@arm.com