Fix a regression in the dca parser introduced by dts express support.

The dca parser needs to check that the framesize is actually of a complete
frame, and not of a partial DTS-HD frame, which is not constant size, and
thus the check would fail.
(cherry picked from commit ebc0ccb9af59b78732e82c09f8c90b1d46b478e0)

Review-by: Benjamin Larsson
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
