Documentation: PCI: endpoint: Fix ntb/vntb copy & paste errors

Documentation: PCI: endpoint: Fix ntb/vntb copy & paste errors

Fix copy & paste errors by changing the references from 'ntb' to 'vntb'.

Fixes: 4ac8c8e52cd9 ("Documentation: PCI: Add specification for the PCI vNTB function device")
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
[mani: squashed the patches and fixed more errors]
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Link: https://patch.msgid.link/b51c2a69ffdbfa2c359f5cf33f3ad2acc3db87e4.1762154911.git.baruch@tkos.co.il