spi: Fix bit assignment with flags

spi: Fix bit assignment with flags

Fixed bit assignment with flags members on spi_slave{}

Cc: Simon Glass <sjg@chromium.org>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
Tested-by: Mugunthan V N <mugunthanvnm@ti.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Jagan Teki <jteki@openedev.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Jagan Teki <jteki@openedev.com>