i2c: designware_i2c: Use an enum for selected speed mode

Group these #defines into an enum to make it easier to understand the
relationship between them.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Jun Chen <ptchentw@gmail.com>
Reviewed-by: Heiko Schocher <hs@denx.de>
diff --git a/drivers/i2c/designware_i2c.c b/drivers/i2c/designware_i2c.c
index dd1cc0b..2416ef3 100644
--- a/drivers/i2c/designware_i2c.c
+++ b/drivers/i2c/designware_i2c.c
@@ -57,10 +57,10 @@
 					   unsigned int speed,
 					   unsigned int bus_mhz)
 {
+	enum i2c_speed_mode i2c_spd;
 	unsigned int cntl;
 	unsigned int hcnt, lcnt;
 	unsigned int ena;
-	int i2c_spd;
 
 	/* Allow high speed if there is no config, or the config allows it */
 	if (speed >= I2C_HIGH_SPEED &&
diff --git a/drivers/i2c/designware_i2c.h b/drivers/i2c/designware_i2c.h
index d4c1ca0..569cab6 100644
--- a/drivers/i2c/designware_i2c.h
+++ b/drivers/i2c/designware_i2c.h
@@ -136,9 +136,13 @@
 #define IC_STATUS_ACT		0x0001
 
 /* Speed Selection */
-#define IC_SPEED_MODE_STANDARD	1
-#define IC_SPEED_MODE_FAST	2
-#define IC_SPEED_MODE_HIGH	3
+enum i2c_speed_mode {
+	IC_SPEED_MODE_STANDARD,
+	IC_SPEED_MODE_FAST,
+	IC_SPEED_MODE_HIGH,
+
+	IC_SPEED_MODE_COUNT,
+};
 
 #define I2C_HIGH_SPEED		3400000
 #define I2C_FAST_SPEED		400000