mtd: rawnand: remove redundant assignment to variable bbtblocks

The variable bbtblocks is being assigned a value that is never
read. The assignment is redundant and can be removed.

Cleans up clang scan build warning:
drivers/mtd/nand/raw/nand_bbt.c:579:3: warning: Value stored to
'bbtblocks' is never read [deadcode.DeadStores]
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20240209174019.3933233-1-colin.i.king@gmail.com

drivers/mtd/nand/raw/nand_bbt.c

@@ -576,7 +576,6 @@ static int search_bbt(struct nand_chip *this, uint8_t *buf,
 		startblock &= bbtblocks - 1;
 	} else {
 		chips = 1;
-		bbtblocks = mtd->size >> this->bbt_erase_shift;
 	}
 
 	for (i = 0; i < chips; i++) {