Make it easier to enter initials with keyboard controls on the high-score page

[spillner]

I noticed that entering initials after a race felt a little fiddly with keyboard controls because OHIScore::do_input() is looking for a fairly large steering signal to shift the selected letter. This patch moderates the steering sensitivity for that page only when the input source is not an analog joystick or gamepad. There are no changes to behavior using a joystick or gamepad, and no changes to actual gameplay regardless of input method.