spi: spi-fsl-dspi: Drop unreachable else if statement

The if statement just above this if/else statement triggers on the same
condition, and then invalidates it.

Signed-off-by: Esben Haabendal <eha@deif.com>
Acked-by: Martin Hundebøll <martin@geanix.com>
Signed-off-by: Mark Brown <broonie@kernel.org>