There is no way to stop the phone from going into "Safe Mode" if the volume button is stuck. It is one of things you need to do (push that button during a start/restart) to get into "Safe Mode".
You can try and use the "Status Bar" to turn off "Safe Mode'. Pull down (swipe) the "Status Bar" of your phone. Now tap the "Safe Mode" button. This should turn "Safe Mode" off.
However, this will also make the phone restart. Which then, of course, would lead back to it being in "Safe Mode".
You need to get the button fixed.