modules: hal_nordic: nrfx: Handle properly I2S0 instance

Although existing nRF SoCs have only one I2S instance, the nrfx_i2s
driver has now multi-instance API and the related nrfx configuration
symbols need to be used appropriately.

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>