ARM: dts: kirkwood: Fix PCIe label on OpenRD

While converting PCIe node on kirkwood by using label, the following
commit eb13cf83 ("ARM: dts: kirkwood: Fixup pcie DT warnings")
introduced a regression on the OpenRD boards: the PCIe didn't work
anymore. As reported by Aaro Koskinen, the display/framebuffer was
lost. This commit adds the forgotten label.

Reported-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Tested-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Fixes: eb13cf83 ("ARM: dts: kirkwood: Fixup pcie DT warnings")
Cc: stable@vger.kernel.org
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>