rme: provide a proper fix in place of the temporary workaround committed in r2384...

rme: provide a proper fix in place of the temporary workaround committed in r2384.  This should restore correct handling of internal and external clocks while avoiding the issues that r2384 circumvented.  In addition, the debug report of the sample rate on start has been moved to resetForStreaming() since this is where 'stat' is being set as of r2077.  Since r2077 the 'rate on start' debug report has been based on an uninitialised variable (note that this issue only affected debug output: the content of 'stat' was not used for anything else within prepare() after r2077).

git-svn-id: svn+ssh://ffado.org/ffado/trunk@2406 2be59082-3212-0410-8809-b0798e1608f0