spi: Return -ENOSYS when system call is not available

Update spi_controller_dma_map_mem_op_data() to use -ENOSYS, which is the
correct error code for U-Boot.
Signed-off-by: NSimon Glass <sjg@chromium.org>

include/spi-mem.h

@@ -222,7 +222,7 @@ spi_controller_dma_map_mem_op_data(struct spi_controller *ctlr,
 				   const struct spi_mem_op *op,
 				   struct sg_table *sg)
 {
-	return -ENOTSUPP;
+	return -ENOSYS;
 }
 
 static inline void