Documentation: PCI: Fix pci_alloc_irq_vectors() function name typo

Documentation/PCI/msi-howto.rst referred to pci_irq_alloc_vectors() when it
should refer to pci_alloc_irq_vectors().  Fix the typo.

Link: https://lore.kernel.org/r/20191230131428.1200-1-yuzenghui@huawei.com
Signed-off-by: Zenghui Yu <yuzenghui@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Andrew Murray <andrew.murray@arm.com>

Documentation/PCI/msi-howto.rst

@@ -283,5 +283,5 @@ or disabled (0).  If 0 is found in any of the msi_bus files belonging
 to bridges between the PCI root and the device, MSIs are disabled.
 
 It is also worth checking the device driver to see whether it supports MSIs.
-For example, it may contain calls to pci_irq_alloc_vectors() with the
+For example, it may contain calls to pci_alloc_irq_vectors() with the
 PCI_IRQ_MSI or PCI_IRQ_MSIX flags.