fixed a eclipse compiling warning:

in fm3_uart.c Line 599
case label value exceeds maximum value for type

git-svn-id: https://rt-thread.googlecode.com/svn/trunk@2152 bbd45198-f89e-11dd-88c7-29a3b14d5316

components/drivers/include/drivers/serial.h

@@ -27,10 +27,10 @@
 #define DATA_BITS_8			8
 #define DATA_BITS_9			9
 
-#define STOP_BITS_1			1
-#define STOP_BITS_2			2
-#define STOP_BITS_3			3
-#define STOP_BITS_4			4
+#define STOP_BITS_1			0
+#define STOP_BITS_2			1
+#define STOP_BITS_3			2
+#define STOP_BITS_4			3
 
 #define PARITY_NONE			0
 #define PARITY_ODD			1