iio:pressure:ms5611: fix ms5607 temp compensation

Computation of sens2 was wrong and is fixed by this patch, sens2 should be:
    2 * (t - 2000)^2
See page 8 of ms5607 datasheet here:
    http://www.meas-spec.com/product/pressure/MS5607-02BA03.aspx

Signed-off-by: Gregor Boirie <gregor.boirie@parrot.com>
Acked-by: Lucas De Marchi <lucas.demarchi@intel.com>
Acked-by: Peter Meerwald-Stadler <pmeerw@pmeerw.net>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/pressure/ms5611_core.c

@@ -136,17 +136,17 @@ static int ms5607_temp_and_pressure_compensate(struct ms5611_chip_info *chip_inf
 
 	t = 2000 + ((chip_info->prom[6] * dt) >> 23);
 	if (t < 2000) {
-		s64 off2, sens2, t2;
+		s64 off2, sens2, t2, tmp;
 
 		t2 = (dt * dt) >> 31;
-		off2 = (61 * (t - 2000) * (t - 2000)) >> 4;
-		sens2 = off2 << 1;
+		tmp = (t - 2000) * (t - 2000);
+		off2 = (61 * tmp) >> 4;
+		sens2 = tmp << 1;
 
 		if (t < -1500) {
-			s64 tmp = (t + 1500) * (t + 1500);
-
+			tmp = (t + 1500) * (t + 1500);
 			off2 += 15 * tmp;
-			sens2 += (8 * tmp);
+			sens2 += 8 * tmp;
 		}
 
 		t -= t2;