Placing an RLC input filter at the input of a buck
First, the filters have two different purposes, unless this were a true two-wire device, and the AOZ1284 is not. 


An input filter


provides a smoothed voltage source to the buck converter.
and it prevents high-frequency harmonics (RF noise) from getting into the supply line.

An output filter eliminates ripple and noise from the output line.


Second, the product description already includes Cin on the schematic; additional series inductance of the filter would be fine, though it would be a good idea to increase the value of Cin, which must come after the filter, and use both large electrolytic and small ceramic caps to insure a low-impedance supply to the IC.