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

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

Fixes: 4774fb0a ("mtd: nand/fsmc: Add DMA support")
Cc: stable@vger.kernel.org
Signed-off-by: Thomas Fourier <fourier.thomas@gmail.com>
Rule: add
Link: https://lore.kernel.org/stable/20250702065806.20983-2-fourier.thomas%40gmail.com


Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>