usb: phy: add MODULE_LICENSE to phy-tegra-usb.c

When this file is built as a module, it needs a MODULE_LICENSE in order
to access many exported symbols.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Felipe Balbi <balbi@ti.com>
Tested-by: Thierry Reding <thierry.reding@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>