mtd: nand: assign reasonable default name for NAND drivers

Commits such as commit 853f1c58 ("mtd: nand: omap2: show parent
device structure in sysfs") attempt to rely on the core MTD code to set
the MTD name based on the parent device. However, nand_base tries to set
a different default name according to the flash name (e.g., extracted
from the ONFI parameter page), which means NAND drivers will never make
use of the MTD defaults. This is not the intention of commit
853f1c58.

This results in problems when trying to use the cmdline partition
parser, since the MTD name is different than expected. Let's fix this by
providing a default NAND name, where possible.

Note that this is not really a great default name in the long run, since
this means that if there are multiple MTDs attached to the same
controller device, they will have the same name. But that is an existing
issue and requires future work on a better controller vs. flash chip
abstraction to fix properly.

Fixes: 853f1c58 ("mtd: nand: omap2: show parent device structure in sysfs")
Reported-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Reviewed-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Tested-by: Heiko Schocher <hs@denx.de>
Cc: Heiko Schocher <hs@denx.de>
Cc: Frans Klaver <fransklaver@gmail.com>
Cc: <stable@vger.kernel.org>

drivers/mtd/nand/nand_base.c

@@ -3996,6 +3996,9 @@ int nand_scan_ident(struct mtd_info *mtd, int maxchips,
 	if (ret)
 		return ret;
 
+	if (!mtd->name && mtd->dev.parent)
+		mtd->name = dev_name(mtd->dev.parent);
+
 	/* Set the default functions */
 	nand_set_defaults(chip, chip->options & NAND_BUSWIDTH_16);