mtd: Add check for devm_kcalloc()

Add a check for devm_kcalloc() to ensure successful allocation.

Fixes: 78c08247b9 ("mtd: Support kmsg dumper based on pstore/blk")
Cc: stable@vger.kernel.org # v5.10+
Signed-off-by: Jiasheng Jiang <jiashengjiangcool@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>

drivers/mtd/mtdpstore.c

@@ -423,6 +423,9 @@ static void mtdpstore_notify_add(struct mtd_info *mtd)
 	longcnt = BITS_TO_LONGS(div_u64(mtd->size, mtd->erasesize));
 	cxt->badmap = devm_kcalloc(&mtd->dev, longcnt, sizeof(long), GFP_KERNEL);
 
+	if (!cxt->rmmap || !cxt->usedmap || !cxt->badmap)
+		return;
+
 	/* just support dmesg right now */
 	cxt->dev.flags = PSTORE_FLAGS_DMESG;
 	cxt->dev.zone.read = mtdpstore_read;