mtd: rawnand: renesas: Add missing check after DMA map

commit 79e441ee upstream.

The DMA map functions can fail and should be tested for errors.

Fixes: d8701fe8 ("mtd: rawnand: renesas: Add new NAND controller driver")
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Fourier <fourier.thomas@gmail.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>