spi: spi_qsd: Prevent transfer grouping

Prevent spi transfers from being grouped together.
Grouping multiple transfers together causes invalid
write then read transactions. This patch prevents
the transactions from being grouped and ensures the
chipselect toggles appropriately.

CRs-Fixed: 661007
Change-Id: I1962cc95fde196295f37c64ecd54e490a7285bc4
Signed-off-by: Dan Sneddon <dsneddon@codeaurora.org>