pci: imx: Add iMX6SX compatible

The driver works fine with iMX6SX, add the missing compatible string.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Bin Meng <bmeng.cn@gmail.com>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>
diff --git a/drivers/pci/pcie_imx.c b/drivers/pci/pcie_imx.c
index d53d629..3621636 100644
--- a/drivers/pci/pcie_imx.c
+++ b/drivers/pci/pcie_imx.c
@@ -815,6 +815,7 @@
 
 static const struct udevice_id imx_pcie_ids[] = {
 	{ .compatible = "fsl,imx6q-pcie" },
+	{ .compatible = "fsl,imx6sx-pcie" },
 	{ }
 };