No functional change. Get "struct pcie_port *" from private data
pointer of "struct irq_domain" in dw_pcie_irq_domain_free() to make
it look similar to how "struct pcie_port *" is obtained in
dw_pcie_irq_domain_alloc()

Link: https://lore.kernel.org/r/20191220100550.777-1-kishon@ti.comSigned-off-by: NKishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: NLorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: NGustavo Pimentel <gustavo.pimentel@synopsys.com>