serial: stm32: change register's offset type from u8 to u16

USART has registers above 0xff offset, so extend variable type to u16.
And change UNDEF_REG to 0xffff.

Signed-off-by: Valentin Caron <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/stm32-usart.h

···
 #define DRIVER_NAME "stm32-usart"
 
 struct stm32_usart_offsets {
-	u8 cr1;
-	u8 cr2;
-	u8 cr3;
-	u8 brr;
-	u8 gtpr;
-	u8 rtor;
-	u8 rqr;
-	u8 isr;
-	u8 icr;
-	u8 rdr;
-	u8 tdr;
-	u8 presc;
+	u16 cr1;
+	u16 cr2;
+	u16 cr3;
+	u16 brr;
+	u16 gtpr;
+	u16 rtor;
+	u16 rqr;
+	u16 isr;
+	u16 icr;
+	u16 rdr;
+	u16 tdr;
+	u16 presc;
 };
 
 struct stm32_usart_config {
···
 	struct stm32_usart_config cfg;
 };
 
-#define UNDEF_REG 0xff
+#define UNDEF_REG 0xffff
 
 /* USART_SR (F4) / USART_ISR (F7) */
 #define USART_SR_PE		BIT(0)