regmap-irq: Fix dereference of a potentially null d->virt_buf

The clean up of struct d can potentiallly index into a null array
d->virt_buf causing errorenous pointer dereferencing issues on
kfree calls.  Fix this by adding a null check on d->virt_buf before
attempting to traverse the array to kfree the objects.

Addresses-Coverity: ("Dereference after null check")
Fixes: 4c501445 ("regmap-irq: Introduce virtual regs to handle more config regs")
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Link: https://lore.kernel.org/r/20210406164002.430221-1-colin.king@canonical.comSigned-off-by: NMark Brown <broonie@kernel.org>

drivers/base/regmap/regmap-irq.c

@@ -901,9 +901,11 @@ int regmap_add_irq_chip_fwnode(struct fwnode_handle *fwnode,
 	kfree(d->mask_buf);
 	kfree(d->status_buf);
 	kfree(d->status_reg_buf);
-	for (i = 0; i < chip->num_virt_regs; i++)
-		kfree(d->virt_buf[i]);
-	kfree(d->virt_buf);
+	if (d->virt_buf) {
+		for (i = 0; i < chip->num_virt_regs; i++)
+			kfree(d->virt_buf[i]);
+		kfree(d->virt_buf);
+	}
 	kfree(d);
 	return ret;
 }