drivers/flash: STM32: use clk dt definitions in h7 flash driver

This commit replaces driver hard coded clk bus and enr definitions with
definitions from device tree.

Signed-off-by: Thomas Stranger <[email protected]>

Author: str4t0m

drivers/flash/flash_stm32h7x.c

@@ -605,8 +605,8 @@ void flash_stm32_page_layout(const struct device *dev,
 
 static struct flash_stm32_priv flash_data = {
 	.regs = (FLASH_TypeDef *) DT_INST_REG_ADDR(0),
-	.pclken = { .bus = STM32_CLOCK_BUS_AHB3,
-		    .enr = LL_AHB3_GRP1_PERIPH_FLASH },
+	.pclken = { .bus = DT_INST_CLOCKS_CELL(0, bus),
+		    .enr = DT_INST_CLOCKS_CELL(0, bits)},
 };
 
 static const struct flash_driver_api flash_stm32h7_api = {