nand: sunxi: Fix modulo by zero error

When trying to autodetect the ECC and randomization configurations, the
driver starts with a randomization disabled and no seeds.

In this case, the number of seeds is obviously 0, and the randomize boolean
is set to false.

However, the logic that retrieves the seed for a given page offset will
blindly use the number of seeds, without testing if the randomization is
enabled, basically doing a modulo by 0.

As it turns out, the libgcc in the common toolchain returns 0 here, which
was our expected value in such a case, and why we would not detect it.
However, U-Boot's libgcc will for some reason return from the function
instead, resulting in an error to load the U-Boot binary in the SPL.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Acked-by: Scott Wood <oss@buserror.net>
Reviewed-by: Jagan Teki <jagan@openedev.com>

drivers/mtd/nand/sunxi_nand_spl.c

@@ -245,7 +245,7 @@ static int nand_read_page(const struct nfc_config *conf, u32 offs,
 {
 	dma_addr_t dst = (dma_addr_t)dest;
 	int nsectors = len / conf->ecc_size;
-	u16 rand_seed;
+	u16 rand_seed = 0;
 	u32 val;
 	int page;
 
@@ -258,8 +258,9 @@ static int nand_read_page(const struct nfc_config *conf, u32 offs,
 	/* clear ecc status */
 	writel(0, SUNXI_NFC_BASE + NFC_ECC_ST);
 
-	/* Choose correct seed */
-	rand_seed = random_seed[page % conf->nseeds];
+	/* Choose correct seed if randomized */
+	if (conf->randomize)
+		rand_seed = random_seed[page % conf->nseeds];
 
 	writel((rand_seed << 16) | (conf->ecc_strength << 12) |
 		(conf->randomize ? NFC_ECC_RANDOM_EN : 0) |