mtd: rawnand: Provide a helper to get chip->data_buf

We plan to move cache related fields to a pagecache struct in nand_chip
but some drivers access ->pagebuf directly to invalidate the cache
before they start using ->data_buf.

Let's provide an helper that returns a pointer to ->data_buf after
invalidating the cache.

Signed-off-by: Boris Brezillon <bbrezillon@kernel.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Frieder Schrempf <frieder.schrempf@kontron.de>
diff --git a/drivers/mtd/nand/raw/nand_bbt.c b/drivers/mtd/nand/raw/nand_bbt.c
index 19a2b56..fff8036 100644
--- a/drivers/mtd/nand/raw/nand_bbt.c
+++ b/drivers/mtd/nand/raw/nand_bbt.c
@@ -901,7 +901,9 @@
 static inline int nand_memory_bbt(struct nand_chip *this,
 				  struct nand_bbt_descr *bd)
 {
-	return create_bbt(this, this->data_buf, bd, -1);
+	u8 *pagebuf = nand_get_data_buf(this);
+
+	return create_bbt(this, pagebuf, bd, -1);
 }
 
 /**