dsp: Avoid configuring PSPD channel mixer if PSPD is already configured

Observing audio glitch issue while trying to apply PSPD
channel mixer coefficients for already applied COPP port.
To fix this, added check condition to retun 0 without
applying PSPD.

Change-Id: I3825cacfd888f153144cc5d73eb274f4fbf5d8bc
Signed-off-by: Ramu Gottipati <ramug@codeaurora.org>