Reorder audio_format fields in sine_wave.c to match declaration of audio_format_t in pico-extras audio.h

[Giuseppe499]

I reordered the audio_format fields in sine_wave.c to match the type declaration of audio_format_t in pico-extras audio.h

This is particularly usefull if a user wants to use C++ instead of C as the wrong ordering will throw the following error at compile time:

error: designator order for field 'audio_format::sample_freq' does not match declaration order in 'audio_format_t' {aka 'audio_format'}

[Giuseppe499]

@kilograham, can I have some feedback?