Add a unreference bo in the error path, to prevent leaking a bo ref.

Return 0 on success to clarify the success path.
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Fixes: 44e69495 ("drm/xe/display: Implement display support")
Cc: <stable@vger.kernel.org> # v6.8+
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240404090302.68422-1-maarten.lankhorst@linux.intel.com