nrf: i2sout: Assign SWIDTH

The sample width register was never set, so all samples were played
as though they were 16 bit.

After this change, 8-bit samples no longer produce audio on the MAX 98357A
BOB, because only 16-, 24-, and 32-bit samples are supported by the
hardware.  This will be addressed by a future change to pad samples to
16 bits; see #2323 and the 98357A datasheet page 6.

ports/nrf/common-hal/audiobusio/I2SOut.c

@@ -246,6 +246,10 @@ void common_hal_audiobusio_i2sout_play(audiobusio_i2sout_obj_t* self,
     self->single_buffer = single_buffer;
     self->samples_signed = samples_signed;
 
+
+    NRF_I2S->CONFIG.SWIDTH = self->bytes_per_sample == 1
+        ? I2S_CONFIG_SWIDTH_SWIDTH_8Bit
+        : I2S_CONFIG_SWIDTH_SWIDTH_16Bit;
     choose_i2s_clocking(self, sample_rate);
     /* Allocate buffers based on a maximum duration
      * This duration was chosen empirically based on what would