spi: spi-fsl-dspi: fix broken DSPI_EOQ_MODE

This patch fixes the dspi_eoq_write function used by the
ColdFire mcf5441x family. The 16 bit cmd part must be re-set at
each data transfer.

Also, now that fifo_size variables are used for eoq_read/write,
a proper fifo size must be set (16 slots for the ColdFire dspi
module version).

Signed-off-by: Angelo Dureghello <angelo@sysam.it>
Acked-by: Esben Haabendal <esben@haabendal.dk>
Signed-off-by: Mark Brown <broonie@kernel.org>
Cc: stable@vger.kernel.org