spi: spi_qsd: Fix the CS logic for multi transfers

In cases of multi transfers the SPI framework sends in the raw CS bit
value to be sent over the line which the driver uses as is. But for
active CS low devices, this means that the driver will end up asserting
CS when it shouldn't be. Change the logic in the driver to check the CS
mode before asserting or deasserting the CS line.

Change-Id: I774d98dbcdf82aa8bb1f289eadab415de717e758
Signed-off-by: Girish Mahadevan <girishm@codeaurora.org>