It is unnecessary to check for whether the number of planes
of an already existing audio pool coincides with the number
of planes to use for the frame: If the common format of both
is planar, then the number of planes coincides with the number
of channels for which there is already a check*; if not,
then both the existing pool as well as the frame use one pool.

*: In fact, one could reuse the pool in this case even if the
number of channels changes.
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>