tests/wavreadertest: Allow the input file to be specified on the command line
tests/wavreadertest: Allow the input file to be specified on the command line

This makes no difference when the test is run as part of the test harness
but allows arbitrary .wav files to be pushed through the DSP.

Signed-off-by: Daniel Thompson <3d0f3b9ddcacec30c4008c5e030e6c13a478cb4f@redfelineninja.org.uk>

daniel-thompson/tintamp,daniel-thompson/tintamp,daniel-thompson/tintamp