spi: fsl-espi: improve message length handling

Move checking for a zero-length message up in the call chain and
use m->frame_length instead of re-calculating the overall length
of all transfers in the message.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
1 file changed