af_hrtf: cosmetics: reindent misaligned code block
af_hrtf: request required samplerate, instead of erroring out

It seems hrtf works in 48khz only - and if that wasn't the input, the
filter just exited with an error. Make it request the 48khz instead. The
player will insert a resampling filter.

Not sure why it wasn't done like this in the first place.