spi: atmel: Fix PDC transfer setup bug

atmel_spi_dma_map_xfer to never be called in PDC mode. This causes the
driver to silently fail.

This patch changes the conditional to match the behaviour of the
previous commit before the refactor.

Fixes: 5fa5e6de ("spi: atmel: Switch to transfer_one transfer method")
Signed-off-by: Ville Baillie <villeb@bytesnap.co.uk>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210921072132.21831-1-villeb@bytesnap.co.uk


Signed-off-by: Mark Brown <broonie@kernel.org>