spi: qup: Do block sized read/write in block mode

This patch corrects the behavior of the BLOCK
transactions.  During block transactions, the controller
must be read/written to in block size transactions.

Signed-off-by: Andy Gross <andy.gross@linaro.org>
Signed-off-by: Varadarajan Narayanan <varada@codeaurora.org>
Signed-off-by: Mark Brown <broonie@kernel.org>