Fix ppm fractional display on finetune Frq page

Fix ppm fractional display on finetune Frq page

The Frq page used remainderf to extract the fractional part of the
correction value, but remainderf rounds to the nearest integer and
returns negative results when the fraction exceeds 0.5. This caused
values like 0.965 ppm to render as " 0-350" instead of " 09650".
Switch to fmodf, matching the DELtA page above.