mtd: rawnand: stm32_fmc2: use timings.mode instead of checking tRC_min

Use timings.mode value instead of checking tRC_min timing
for EDO mode support.

Signed-off-by: Christophe Kerello <christophe.kerello@foss.st.com>
Fixes: 2cd457f3 ("mtd: rawnand: stm32_fmc2: add STM32 FMC2 NAND flash controller driver")
Cc: stable@vger.kernel.org #v5.10+
Reviewed-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Link: https://lore.kernel.org/linux-mtd/20230328155819.225521-3-christophe.kerello@foss.st.com