scripts: dts: Fix generation of -name properties.

If we have something like dma-names we should ended up generating
something like:

  DT_ST_STM32_I2S_40015000_RX_DMAS_CONTROLLER_1

This isn't quite what we expect.  We should instead get:

  DT_ST_STM32_I2S_40015000_RX_DMAS_CONTROLLER
  DT_ST_STM32_I2S_40015000_DMAS_CONTROLLER_1

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>