mtd: rawnand: jz4740: group nand_scan_{ident, tail} calls

Prepare the migration to nand_scan() by moving both calls to
nand_scan_ident() and nand_scan_tail() in a single spot.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>