8250_ni16550: fix compiler warning about mixed declarations and code

During the build the following compiler warning is printed:

drivers/tty/serial/8250/8250_ni16550.c: In function ‘ni16550_config_prescaler’:
drivers/tty/serial/8250/8250_ni16550.c:181:2: warning: ISO C90 forbids mixed declarations and code [-Wdeclaration-after-statement]
  181 |  uint8_t efr_value;

Fix it by moving the declaration of 'efr_value' at the beginning of the
function.

Signed-off-by: Gratian Crisan <gratian.crisan@ni.com>

Author: gratian

drivers/tty/serial/8250/8250_ni16550.c

@@ -174,12 +174,11 @@ void ni16550_config_prescaler(unsigned long iobase, uint8_t prescaler)
 	 * Sets EFR[4] for Enhanced Mode.
 	 */
 	uint8_t lcr_value;
+	uint8_t efr_value;
 
 	lcr_value = inb(iobase + UART_LCR);
 	outb(UART_LCR_CONF_MODE_B, iobase + UART_LCR);
 
-	uint8_t efr_value;
-
 	efr_value = inb(iobase + UART_EFR);
 	efr_value |= UART_EFR_ECB;