serial: serial_stm32: Rename status register flags

Uart status register is named USART_ISR on STM32F7, STM32H7
and STM32MP1 SoCs family, but USART_SR only on STM32F4 SoCs.

Use USART_ISR_ prefix instead of USART_SR_ .

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
diff --git a/drivers/serial/serial_stm32.h b/drivers/serial/serial_stm32.h
index 42fb132..6ebec0a 100644
--- a/drivers/serial/serial_stm32.h
+++ b/drivers/serial/serial_stm32.h
@@ -60,9 +60,9 @@
 
 #define USART_CR3_OVRDIS		BIT(12)
 
-#define USART_SR_FLAG_ORE		BIT(3)
-#define USART_SR_FLAG_RXNE		BIT(5)
-#define USART_SR_FLAG_TXE		BIT(7)
+#define USART_ISR_FLAG_ORE		BIT(3)
+#define USART_ISR_FLAG_RXNE		BIT(5)
+#define USART_ISR_FLAG_TXE		BIT(7)
 
 #define USART_BRR_F_MASK		GENMASK(7, 0)
 #define USART_BRR_M_SHIFT		4