PCI: vmd: Fix malformed Kconfig default

'default N' should be 'default n', though they happen to have the same
effect here, due to undefined symbols (N in this case) evaluating to n
in a tristate sense.

Remove the default instead of changing it. bool and tristate symbols
implicitly default to n.

Signed-off-by: Ulf Magnusson <ulfalizer@gmail.com>
[lorenzo.pieralisi@arm.com: updated commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>