PCI: Provide pci_free_irq_vectors() stub

473b9f3 ("rust: pci: fix build failure when CONFIG_PCI_MSI is
disabled") fixed a build error by providing Rust helpers when
CONFIG_PCI_MSI is not set. However the Rust helpers rely on
pci_free_irq_vectors(), which is only available when CONFIG_PCI=y.

When CONFIG_PCI is not set, there is already a stub for
pci_alloc_irq_vectors().  Add a similar stub for pci_free_irq_vectors().

Fixes: 473b9f3 ("rust: pci: fix build failure when CONFIG_PCI_MSI is disabled")
Reported-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Closes: https://lore.kernel.org/rust-for-linux/20251209014312.575940-1-fujita.tomonori@gmail.com/
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202512220740.4Kexm4dW-lkp@intel.com/
Reported-by: Liang Jie <liangjie@lixiang.com>
Closes: https://lore.kernel.org/rust-for-linux/20251222034415.1384223-1-buaajxlj@163.com/
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Drew Fustini <fustini@kernel.org>
Reviewed-by: David Gow <davidgow@google.com>
Reviewed-by: Joel Fernandes <joelagnelf@nvidia.com>
Reviewed-by: Danilo Krummrich <dakr@kernel.org>
Link: https://patch.msgid.link/20251226113938.52145-1-boqun.feng@gmail.com

Author: fbq

include/linux/pci.h

@@ -2210,6 +2210,10 @@ pci_alloc_irq_vectors(struct pci_dev *dev, unsigned int min_vecs,
 {
 	return -ENOSPC;
 }
+
+static inline void pci_free_irq_vectors(struct pci_dev *dev)
+{
+}
 #endif /* CONFIG_PCI */
 
 /* Include architecture-dependent settings and functions */