mtd: rawnand: cadence: Make cadence_nand_attach_chip static

Fix sparse warning:

drivers/mtd/nand/raw/cadence-nand-controller.c:2595:5:
 warning: symbol 'cadence_nand_attach_chip' was not declared. Should it be static?
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20200410115228.30440-1-yuehaibing@huawei.com

drivers/mtd/nand/raw/cadence-nand-controller.c

@@ -2592,7 +2592,7 @@ cadence_nand_setup_data_interface(struct nand_chip *chip, int chipnr,
 	return 0;
 }
 
-int cadence_nand_attach_chip(struct nand_chip *chip)
+static int cadence_nand_attach_chip(struct nand_chip *chip)
 {
 	struct cdns_nand_ctrl *cdns_ctrl = to_cdns_nand_ctrl(chip->controller);
 	struct cdns_nand_chip *cdns_chip = to_cdns_nand_chip(chip);