PCI: Declare pci_filp_private only when HAVE_PCI_MMAP

The struct pci_filp_private has no users outside drivers/pci/proc.c and is
only used when HAVE_PCI_MMAP is defined.

Wrap the struct pci_filp_private definition itself in #ifdef HAVE_PCI_MMAP.

Found by cppcheck:

  $ cppcheck --enable=all --force drivers/pci/proc.c
  drivers/pci/proc.c:192:6: style: struct member 'pci_filp_private::write_combine' is never used. [unusedStructMember]

Link: https://lore.kernel.org/r/20210706003145.3054881-1-kw@linux.com
Signed-off-by: Krzysztof Wilczyński <kw@linux.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

Author: kwilczynski

drivers/pci/proc.c

@@ -188,10 +188,12 @@ static ssize_t proc_bus_pci_write(struct file *file, const char __user *buf,
 	return nbytes;
 }
 
+#ifdef HAVE_PCI_MMAP
 struct pci_filp_private {
 	enum pci_mmap_state mmap_state;
 	int write_combine;
 };
+#endif /* HAVE_PCI_MMAP */
 
 static long proc_bus_pci_ioctl(struct file *file, unsigned int cmd,
 			       unsigned long arg)