mtd: fsl-quadspi: Fix module unbound

When removing the fsl-quadspi module and running 'cat /proc/mtd' afterwards,
we see garbage data like:

$ rmmod fsl-quadspi
$ cat /proc/mtd
dev: size erasesize name
mtd0: 00000000 00000000 "(null)"
mtd0: 00000000 00000000 "(null)"
mtd0: 00000000 00000000 "(null)"
...
mtd0: a22296c6c756e28 00000000 "(null)"
mtd0: a22296c6c756e28 3064746d "(null)"

If we continue doing multiple module load/unload operations, then it will also
lead to a kernel crash.

The reason for this is due to the wrong mtd index used in
mtd_device_unregister() in the remove function.

We need to keep the mtd unregister index aligned with the one used in the probe
function, which means we need to take into account the 'has_second_chip'
property. By doing so we can guarantee that the mtd index is the same in the
registration and unregistration functions.

With this patch applied we can load/unload the fsl-quadspi driver several times
and it will result in no crash.

Signed-off-by: Fabio Estevam <[e-mail]>
Acked-by: Huang Shijie <[e-mail]>
Tested-by: Frank Li <[e-mail]>
Acked-by: Allen Xu <[e-mail]>
Signed-off-by: Brian Norris <[e-mail]>

drivers/mtd/spi-nor/fsl-quadspi.c

···
 	u32 nor_num;
 	u32 clk_rate;
 	unsigned int chip_base_addr; /* We may support two chips. */
+	bool has_second_chip;
 };
 
 static inline int is_vybrid_qspi(struct fsl_qspi *q)
···
 	struct spi_nor *nor;
 	struct mtd_info *mtd;
 	int ret, i = 0;
-	bool has_second_chip = false;
 	const struct of_device_id *of_id =
 			of_match_device(fsl_qspi_dt_ids, &pdev->dev);
 
···
 		goto irq_failed;
 
 	if (of_get_property(np, "fsl,qspi-has-second-chip", NULL))
-		has_second_chip = true;
+		q->has_second_chip = true;
 
 	/* iterate the subnodes. */
 	for_each_available_child_of_node(dev->of_node, np) {
 		char modalias[40];
 
 		/* skip the holes */
-		if (!has_second_chip)
+		if (!q->has_second_chip)
 			i *= 2;
 
 		nor = &q->nor[i];
···
 	return 0;
 
 last_init_failed:
-	for (i = 0; i < q->nor_num; i++)
+	for (i = 0; i < q->nor_num; i++) {
+		/* skip the holes */
+		if (!q->has_second_chip)
+			i *= 2;
 		mtd_device_unregister(&q->mtd[i]);
-
+	}
 irq_failed:
 	clk_disable_unprepare(q->clk);
 clk_failed:
···
 	struct fsl_qspi *q = platform_get_drvdata(pdev);
 	int i;
 
-	for (i = 0; i < q->nor_num; i++)
+	for (i = 0; i < q->nor_num; i++) {
+		/* skip the holes */
+		if (!q->has_second_chip)
+			i *= 2;
 		mtd_device_unregister(&q->mtd[i]);
+	}
 
 	/* disable the hardware */
 	writel(QUADSPI_MCR_MDIS_MASK, q->iobase + QUADSPI_MCR);