ds2760_battery: Fix integer overflow for time_to_empty_now

On the device we're currently developing, battery sizes of ~2.8Ah and
current flow of ~600mA are typical.

With that values, the life_sec computation overflows due to the
multiplication by 3600.

Signed-off-by: Daniel Mack <[e-mail]>
Cc: Szabolcs Gyurko <[e-mail]>
Cc: Matt Reimer <[e-mail]>
Signed-off-by: Anton Vorontsov <[e-mail]>

drivers/power/ds2760_battery.c

···
 	if (di->rem_capacity > 100)
 		di->rem_capacity = 100;
 
-	if (di->current_uA)
-		di->life_sec = -((di->accum_current_uAh - di->empty_uAh) *
-				 3600L) / di->current_uA;
+	if (di->current_uA >= 100L)
+		di->life_sec = -((di->accum_current_uAh - di->empty_uAh) * 36L)
+					/ (di->current_uA / 100L);
 	else
 		di->life_sec = 0;