PCI: endpoint: pci-epf-test: Don't free doorbell IRQ unless requested

PCI: endpoint: pci-epf-test: Don't free doorbell IRQ unless requested

pci_epf_test_doorbell_cleanup() unconditionally calls free_irq() for the
doorbell virq, which can trigger "Trying to free already-free IRQ"
warnings when the IRQ was never requested or when request_threaded_irq()
failed.

Move free_irq() out of pci_epf_test_doorbell_cleanup() and invoke it
only after a successful request, so that free_irq() is not called for
an unrequested IRQ.

Fixes: eff0c286aa91 ("PCI: endpoint: pci-epf-test: Add doorbell test support")
Signed-off-by: Koichiro Den <den@valinux.co.jp>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Niklas Cassel <cassel@kernel.org>
Link: https://patch.msgid.link/20260217063856.3759713-3-den@valinux.co.jp