spi/s3c64xx: Remove unused message queue

Since the driver has been converted to use the core message pump code
the only use of the messsage queue in the driver is a check to see if
it is empty which will always succeed since nothing ever adds to the
queue. Just remove the queue.

Signed-off-by: Mark Brown <broonie@linaro.org>
Acked-by: Kukjin Kim <kgene.kim@samsung.com>