audio: rename variables in audio_pcm_sw_write()

audio: rename variables in audio_pcm_sw_write()

The audio_pcm_sw_write() function uses a lot of very unspecific
variable names. Rename them for better readability.

ret => total_in
total => total_out
size => buf_len
hwsamples => hw->mix_buf.size
samples => frames_in_max

Acked-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Volker Rümelin <vr_qemu@t-online.de>
Message-Id: <20230224190555.7409-6-vr_qemu@t-online.de>