PCI: xilinx: Fix NULL pointer dereference in xilinx_pcie_intr_handler()

f29861aa301c5 ("PCI: xilinx: Switch to msi_create_parent_irq_domain()")
changed xilinx_pcie::msi_domain from child devices' interrupt domain to
Xilinx AXI bridge's interrupt domain.

However, xilinx_pcie_intr_handler() wasn't changed and still reads Xilinx
AXI bridge's interrupt domain from xilinx_pcie::msi_domain->parent. This
pointer is NULL now.

Update xilinx_pcie_intr_handler() to read the correct interrupt domain
pointer.

Fixes: f29861aa301c5 ("PCI: xilinx: Switch to msi_create_parent_irq_domain()")
Signed-off-by: Nam Cao <[e-mail]>
Signed-off-by: Bjorn Helgaas <[e-mail]>
Link: https://patch.msgid.link/[e-mail]

drivers/pci/controller/pcie-xilinx.c

···
 		if (val & XILINX_PCIE_RPIFR1_MSI_INTR) {
 			val = pcie_read(pcie, XILINX_PCIE_REG_RPIFR2) &
 				XILINX_PCIE_RPIFR2_MSG_DATA;
-			domain = pcie->msi_domain->parent;
+			domain = pcie->msi_domain;
 		} else {
 			val = (val & XILINX_PCIE_RPIFR1_INTR_MASK) >>
 				XILINX_PCIE_RPIFR1_INTR_SHIFT;