mtd: stm32: use parameter instead of default value

To set wait state, a hard coded value is used instead of using
latency parameter. stm32_flash_latency_cfg() is currently used
in arch/arm/mach-stm32/stm32f4/clock.c and in
drivers/clk/clk_stm32f7.c with, in both case, "5" as parameter.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>

drivers/mtd/stm32_flash.c

@@ -17,7 +17,7 @@ flash_info_t flash_info[CONFIG_SYS_MAX_FLASH_BANKS];
 void stm32_flash_latency_cfg(int latency)
 {
 	/* 5 wait states, Prefetch enabled, D-Cache enabled, I-Cache enabled */
-	writel(FLASH_ACR_WS(5) | FLASH_ACR_PRFTEN | FLASH_ACR_ICEN
+	writel(FLASH_ACR_WS(latency) | FLASH_ACR_PRFTEN | FLASH_ACR_ICEN
 		| FLASH_ACR_DCEN, &STM32_FLASH->acr);
 }