mtd: rawnand: stm32_fmc2: avoid warnings when building with W=1 option

This patch solves warnings detected by setting W=1 when building.

Warnings type detected:
drivers/mtd/nand/raw/stm32_fmc2_nand.c: In function ‘stm32_fmc2_calc_timings’:
drivers/mtd/nand/raw/stm32_fmc2_nand.c:1417:23: warning: comparison is
always false due to limited range of data type [-Wtype-limits]
  else if (tims->twait > FMC2_PMEM_PATT_TIMING_MASK)

Signed-off-by: Christophe Kerello <christophe.kerello@st.com>
Cc: stable@vger.kernel.org
Fixes: 2cd457f3 ("mtd: rawnand: stm32_fmc2: add STM32 FMC2 NAND flash controller driver")
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>