ARM: dts: nspire: Fix vbus_reg node to conform with DT binding

This node does not follow the DT binding schema, correct this.
All "regulator-fixed" are voltage type, so drop "regulator-type".
Should result in no functional change.

Signed-off-by: Andrew Davis <afd@ti.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>