mtd: rawnand: omap2: Pass the parent of pdev to dma_request_chan()

Commit e1e6255c ("mtd: rawnand: omap2: convert driver to
nand_scan()") moved part of the init code in the ->attach_chip hook
and at the same time changed the struct device object passed to
dma_request_chan() (&pdev->dev instead of pdev->dev.parent).

Fixes: e1e6255c ("mtd: rawnand: omap2: convert driver to nand_scan()")
Reported-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
Tested-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>