spi: xspips: Fix erranious chipselect togle

Fixed the bug in driver that erraniously disable and enable the
controller while the transfer is in progress and causes the
chip select toggle in between the transfer.

Signed-off-by: Punnaiah Choudary Kalluri <punnaia@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
(cherry picked from commit eb32d1878103f38004374645704212c2985f52f2)