mtd: nand: Drop mtd.owner requirement in nand_scan

Since commit 807f16d4db95 ("mtd: core: set some defaults
when dev.parent is set"), it's now legal for drivers
to call nand_scan and nand_scan_ident without setting
mtd.owner.

Drop the check and while at it remove the BUG() abuse.

Fixes: 807f16d4db95 ("mtd: core: set some defaults when dev.parent is set")
Signed-off-by: Ezequiel Garcia <[e-mail]>
Acked-by: Boris Brezillon <[e-mail]>
[Brian: editorial note - while commit 807f16d4db95 wasn't explicitly
broken, some follow-up commits in the v4.4 release broke a few
drivers, since they would hit this BUG() if they used nand_scan()
and were built as modules]
Signed-off-by: Brian Norris <[e-mail]>

drivers/mtd/nand/nand_base.c

···
  * This is the first phase of the normal nand_scan() function. It reads the
  * flash ID and sets up MTD fields accordingly.
  *
- * The mtd->owner field must be set to the module of the caller.
  */
 int nand_scan_ident(struct mtd_info *mtd, int maxchips,
 		    struct nand_flash_dev *table)
···
  *
  * This fills out all the uninitialized function pointers with the defaults.
  * The flash ID is read and the mtd/chip structures are filled with the
- * appropriate values. The mtd->owner field must be set to the module of the
- * caller.
+ * appropriate values.
  */
 int nand_scan(struct mtd_info *mtd, int maxchips)
 {
 	int ret;
-
-	/* Many callers got this wrong, so check for it for a while... */
-	if (!mtd->owner && caller_is_module()) {
-		pr_crit("%s called with NULL mtd->owner!\n", __func__);
-		BUG();
-	}
 
 	ret = nand_scan_ident(mtd, maxchips, NULL);
 	if (!ret)