PCI: endpoint: Fix a Kconfig prompt of vNTB driver

vNTB driver and NTB driver have same Kconfig prompt. Changed to make it
distinguishable.

Link: https://lore.kernel.org/r/[e-mail]
Fixes: e35f56bb0330 ("PCI: endpoint: Support NTB transfer between RC and EP")
Signed-off-by: Shunsuke Mie <[e-mail]>
Signed-off-by: Lorenzo Pieralisi <[e-mail]>
Signed-off-by: Bjorn Helgaas <[e-mail]>
Reviewed-by: Manivannan Sadhasivam <[e-mail]>

drivers/pci/endpoint/functions/Kconfig

···
 	  If in doubt, say "N" to disable Endpoint NTB driver.
 
 config PCI_EPF_VNTB
-	tristate "PCI Endpoint NTB driver"
+	tristate "PCI Endpoint Virtual NTB driver"
 	depends on PCI_ENDPOINT
 	depends on NTB
 	select CONFIGFS_FS