mtd: maps: fix error return code of physmap_flash_remove()

When platform_get_drvdata() returns NULL to info, no error return code
of physmap_flash_remove() is assigned.
To fix this bug, err is assigned with -EINVAL in this case

Fixes: 73566edf9b91 ("[MTD] Convert physmap to platform driver")
Reported-by: TOTE Robot <[e-mail]>
Signed-off-by: Jia-Ju Bai <[e-mail]>
Signed-off-by: Miquel Raynal <[e-mail]>
Link: https://lore.kernel.org/linux-mtd/[e-mail]

drivers/mtd/maps/physmap-core.c

···
 	int i, err = 0;
 
 	info = platform_get_drvdata(dev);
-	if (!info)
+	if (!info) {
+		err = -EINVAL;
 		goto out;
+	}
 
 	if (info->cmtd) {
 		err = mtd_device_unregister(info->cmtd);