boards: fixed SPI DTS bug for nrf5340_audio_dk board

This fixes the SPI DTS bug on the nrf5340_audio_dk board
which was introduced by b8978e9e:
unit address and first address in 'reg' (0x0) don't match
for /soc/peripheral@50000000/spi@a000/sdhc@1
unit address and first address in 'reg' (0x1) don't match
for /soc/peripheral@50000000/spi@a000/cs47l63@2

Signed-off-by: Tim Sørensen <tims@demant.com>