Input: elan_i2c_smbus - cast sizeof to int for comparison

Comparing an int to a size, which is unsigned, causes the int to become
unsigned, giving the wrong result.  i2c_smbus_read_block_data can return the
result of i2c_smbus_xfer, whih can return a negative error code.

A simplified version of the semantic match that finds this problem is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
@@
int x;
expression e,e1;
identifier f;
@@

*x = f(...);
... when != x = e1
    when != if (x < 0 || ...) { ... return ...; }
*x < sizeof(e)
// </smpl>
Signed-off-by: NJulia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: NDmitry Torokhov <dmitry.torokhov@gmail.com>

drivers/input/mouse/elan_i2c_smbus.c

@@ -387,7 +387,7 @@ static int elan_smbus_prepare_fw_update(struct i2c_client *client)
 		len = i2c_smbus_read_block_data(client,
 						ETP_SMBUS_IAP_PASSWORD_READ,
 						val);
-		if (len < sizeof(u16)) {
+		if (len < (int)sizeof(u16)) {
 			error = len < 0 ? len : -EIO;
 			dev_err(dev, "failed to read iap password: %d\n",
 				error);