vgaarbiter: fix a typo in the vgaarbiter Documentation

I detected a typo, while reading "Documentation/vgaarbiter.txt".  Fix the
'fieldd' mispelling.
Signed-off-by: Detlef Riekenberg <wine.dev@web.de>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>

Documentation/vgaarbiter.txt

@@ -103,7 +103,7 @@ I.2 libpciaccess
 ----------------
 
 To use the vga arbiter char device it was implemented an API inside the
-libpciaccess library. One fieldd was added to struct pci_device (each device
+libpciaccess library. One field was added to struct pci_device (each device
 on the system):
 
     /* the type of resource decoded by the device */