just put your finger on the home button when the screen is awake (whether it is asking for pin/pattern). and make sure that fingerprint you are using has no application set in the fingerprint settings so the function of it is to unlock only.
if you are annoyed the phone asking for pin/pattern instead of a fingerprint, just DO NOT swipe the screen. just double tap for screen to wake, then put your fingerprint on the home button (no need to press if the screen is awake). never swipe the screen so it wont ask a pattern/pin, if that happens, you can still use fingerprint to unlock by just putting your fingerprint in the home button.