spi: pass correct buffer to spi driver given NULL to spi_transceive

When pass NULL to spi_transceive with user space enabled, stack buffer
is still passed to spi driver and it will cause kinds of problems like
MPU fault, so change it to pass relevant NULL pointers in the actual
transceive call.

Fixes: #20811.

Signed-off-by: Wentong Wu <wentong.wu@intel.com>