altera_uart: Adjust the declaration of debug_uart_init()

Follow commit 97b059730218 ("debug_uart: Adjust the declaration of
debug_uart_init()")

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>
Reviewed-by: Marek Vasut <marex@denx.de>
Reviewed-by: Chin Liang See <clsee@altera.com>
diff --git a/drivers/serial/altera_uart.c b/drivers/serial/altera_uart.c
index 4c4794e..5d76c33 100644
--- a/drivers/serial/altera_uart.c
+++ b/drivers/serial/altera_uart.c
@@ -124,7 +124,7 @@
 
 #include <debug_uart.h>
 
-void debug_uart_init(void)
+static inline void _debug_uart_init(void)
 {
 	struct altera_uart_regs *regs = (void *)CONFIG_DEBUG_UART_BASE;
 	u32 div;