PCI: rcar: Fix GPL v2 license string typo

Per license_is_gpl_compatible(), the MODULE_LICENSE() string for GPL v2 is
"GPL v2", not "GPLv2".  Use "GPL v2" so this module doesn't taint the
kernel.

Based-on-work-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>