spi: altera: Change to dynamic allocation of spi id

The spi-altera driver has two flavors: platform and dfl. I'm seeing
a case where I have both device types in the same machine, and they
are conflicting on the SPI ID:

... kernel: couldn't get idr
... kernel: WARNING: CPU: 28 PID: 912 at drivers/spi/spi.c:2920 spi_register_controller.cold+0x84/0xc0a

Both the platform and dfl drivers use the parent's driver ID as the SPI
ID. In the error case, the parent devices are dfl_dev.4 and
subdev_spi_altera.4.auto. When the second spi-master is created, the
failure occurs because the SPI ID of 4 has already been allocated.

Change the ID allocation to dynamic (by initializing bus_num to -1) to
avoid duplicate SPI IDs.

Signed-off-by: Russ Weight <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

drivers/spi/spi-altera-dfl.c

···
 	if (!master)
 		return -ENOMEM;
 
-	master->bus_num = dfl_dev->id;
+	master->bus_num = -1;
 
 	hw = spi_master_get_devdata(master);
 

drivers/spi/spi-altera-platform.c

···
 		return err;
 
 	/* setup the master state. */
-	master->bus_num = pdev->id;
+	master->bus_num = -1;
 
 	if (pdata) {
 		if (pdata->num_chipselect > ALTERA_SPI_MAX_CS) {