mtd: rawnand: denali: do not pass zero maxchips to nand_scan()

Commit 49aa76b ("mtd: rawnand: do not execute nand_scan_ident()
if maxchips is zero") gave a new meaning for calling nand_scan_ident()
with maxchips=0.

It is a special usage for some drivers such as docg4, but actually
the Denali driver may pass maxchips=0 to nand_scan() when the driver
is enabled but no NAND chip is found on the board for some reasons.

If nand_scan_with_ids() is called with maxchips=0, nand_scan_ident()
is skipped, then nand_set_defaults() is skipped as well.  Thus, the
driver must set chip->controller beforehand.  Otherwise, nand_attach()
causes NULL pointer dereference.

In fact, the Denali controller knows the number of connected chips
before calling nand_scan_ident(); if DEVICE_RESET fails, there is no
chip in that chip select.  Then, denali_reset_banks() sets the maxchips
to the number of detected chips.  If no chip is found, maxchips is zero.

In this case, there is no point for calling nand_scan() because we know
it will fail for sure.  Let's make the probe function fail immediately.

Fixes: 49aa76b ("mtd: rawnand: do not execute nand_scan_ident() if maxchips is zero")
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>

drivers/mtd/nand/raw/denali.c

@@ -1338,6 +1338,11 @@ int denali_init(struct denali_nand_info *denali)
 
 	denali_enable_irq(denali);
 	denali_reset_banks(denali);
+	if (!denali->max_banks) {
+		/* Error out earlier if no chip is found for some reasons. */
+		ret = -ENODEV;
+		goto disable_irq;
+	}
 
 	denali->active_bank = DENALI_INVALID_BANK;