Documentation: pci.txt: fix typo

Doubled 'not'.
Signed-off-by: Kulikov Vasiliy <segooon@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

Documentation/PCI/pci.txt

@@ -581,7 +581,7 @@ to be handled by platform and generic code, not individual drivers.
 8. Vendor and device identifications
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-One is not not required to add new device ids to include/linux/pci_ids.h.
+One is not required to add new device ids to include/linux/pci_ids.h.
 Please add PCI_VENDOR_ID_xxx for vendors and a hex constant for device ids.
 
 PCI_VENDOR_ID_xxx constants are re-used. The device ids are arbitrary