PCI: endpoint: pci-epf-vntb: Return -ERANGE for out-of-range MW index

PCI: endpoint: pci-epf-vntb: Return -ERANGE for out-of-range MW index

The mw1..mw4 configfs attributes are only valid when the MW index is
within the configured num_mws range. Return -ERANGE instead of -EINVAL
when a configfs MW size attribute is accessed with an out-of-range MW
index.

Suggested-by: Manivannan Sadhasivam <mani@kernel.org>
Signed-off-by: Koichiro Den <den@valinux.co.jp>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Link: https://patch.msgid.link/20260219145633.4191325-1-den@valinux.co.jp