mtd: rawnand: denali_dt: use dev as a shorthand of &pdev->dev

The probe function references &pdev->dev many times, and I will add
more soon.  Add 'dev' as a shorthand.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Richard Weinberger <richard@nod.at>
Tested-by: Richard Weinberger <richard@nod.at>
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>