PCI/MSI: Fix pci_msix_vec_count() htmldocs failure

An empty line in msi.c caused "make htmldocs" failure:

  Warning(/home/iida/Repo/linux-next//drivers/pci/msi.c:962): bad line:

Fixes: ff1aa430 ("PCI/MSI: Add pci_msix_vec_count()")
Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>