mtd: rawnand: stm32_fmc2: Fix dma_map_sg error check

mtd: rawnand: stm32_fmc2: Fix dma_map_sg error check

dma_map_sg return 0 on error, in case of error return -EIO.

Cc: Miquel Raynal <miquel.raynal@bootlin.com>
Cc: Richard Weinberger <richard@nod.at>
Cc: Vignesh Raghavendra <vigneshr@ti.com>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Cc: Alexandre Torgue <alexandre.torgue@foss.st.com>
Cc: Philipp Zabel <p.zabel@pengutronix.de>
Cc: Christophe Kerello <christophe.kerello@foss.st.com>
Cc: Cai Huoqing <cai.huoqing@linux.dev>
Cc: linux-mtd@lists.infradead.org
Cc: linux-stm32@st-md-mailman.stormreply.com
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Jack Wang <jinpu.wang@ionos.com>
Reviewed-by: Christophe Kerello <christophe.kerello@foss.st.com>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20220819060801.10443-5-jinpu.wang@ionos.com