hwmon: Prevent some divide by zeros in FAN_TO_REG()

The "rpm * div" operations can overflow here, so this patch adds an
upper limit to rpm to prevent that.  Jean Delvare helped me with this
patch.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Roger Lucas <vt8231@hiddenengine.co.uk>
Cc: stable@vger.kernel.org
Signed-off-by: Jean Delvare <khali@linux-fr.org>

drivers/hwmon/lm78.c

diff --git a/drivers/hwmon/lm78.c b/drivers/hwmon/lm78.c
index 6cf6bff..a2f3b4a 100644
--- a/drivers/hwmon/lm78.c
+++ b/drivers/hwmon/lm78.c
@@ -94,6 +94,8 @@
 {
 	if (rpm <= 0)
 		return 255;
+	if (rpm > 1350000)
+		return 1;
 	return clamp_val((1350000 + rpm * div / 2) / (rpm * div), 1, 254);
 }
 

drivers/hwmon/sis5595.c

diff --git a/drivers/hwmon/sis5595.c b/drivers/hwmon/sis5595.c
index 1404e63..72a8897 100644
--- a/drivers/hwmon/sis5595.c
+++ b/drivers/hwmon/sis5595.c
@@ -141,6 +141,8 @@
 {
 	if (rpm <= 0)
 		return 255;
+	if (rpm > 1350000)
+		return 1;
 	return clamp_val((1350000 + rpm * div / 2) / (rpm * div), 1, 254);
 }
 

drivers/hwmon/vt8231.c

diff --git a/drivers/hwmon/vt8231.c b/drivers/hwmon/vt8231.c
index 0e70178..aee14e2 100644
--- a/drivers/hwmon/vt8231.c
+++ b/drivers/hwmon/vt8231.c
@@ -145,7 +145,7 @@
  */
 static inline u8 FAN_TO_REG(long rpm, int div)
 {
-	if (rpm == 0)
+	if (rpm <= 0 || rpm > 1310720)
 		return 0;
 	return clamp_val(1310720 / (rpm * div), 1, 255);
 }