i2c/tsl2550: Fix lux value in dark environment

I've tested TSL2550 driver and I've found a bug: when light is off, 
returned value from tsl2550_calculate_lux function is -1 when it should 
be 0 (sensor correctly read that light was off).

I think the bug is that a zero c0 value (approximated value of ch0) is 
misinterpreted as an error. 

Signed-off-by: Michele Jr De Candia <michele.decandia@valueteam.com>
Acked-by: Rodolfo Giometti <giometti@linux.it>
Signed-off-by: Jean Delvare <khali@linux-fr.org>

drivers/i2c/chips/tsl2550.c

@@ -27,7 +27,7 @@
 #include <linux/delay.h>
 
 #define TSL2550_DRV_NAME	"tsl2550"
-#define DRIVER_VERSION		"1.1.1"
+#define DRIVER_VERSION		"1.1.2"
 
 /*
  * Defines
@@ -189,13 +189,16 @@ static int tsl2550_calculate_lux(u8 ch0, u8 ch1)
 	u8 r = 128;
 
 	/* Avoid division by 0 and count 1 cannot be greater than count 0 */
-	if (c0 && (c1 <= c0))
-		r = c1 * 128 / c0;
+	if (c1 <= c0)
+		if (c0) {
+			r = c1 * 128 / c0;
+
+			/* Calculate LUX */
+			lux = ((c0 - c1) * ratio_lut[r]) / 256;
+		} else
+			lux = 0;
 	else
-		return -1;
-
-	/* Calculate LUX */
-	lux = ((c0 - c1) * ratio_lut[r]) / 256;
+		return -EAGAIN;
 
 	/* LUX range check */
 	return lux > TSL2550_MAX_LUX ? TSL2550_MAX_LUX : lux;