[pvr] fix the path split-up in CPVRTimers::GetDirectory() which results in no timer is returned

On windows the `URIUtils::SplitPath(URIUtils::GetDirectory(fileName))` don't return the right count of elements which prevents the method to return the exsting timers. The root cause is that `URIUtils::SplitPath()` use the OS dependent directory separator, but the path given to `SplitPath()` holds slashes (/). I've removed the different path preparations and split `strPath` directly which results in a vector -> [0]: pvr://, [1]: timers, [2]: tv or radio.