Since we are using the 'hw' interface of ALSA, we don't have the luxury of
samplerate conversion, given by the 'plughw' interface. If we try to set a
samplerate that is not supported, ALSA will just throw an error.
We can test for the supported samplerates, and create a list of supported
samplerates, then limit the selection to only those values. The frontend can
query the list of supported samplerates.
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>