ASoC: trivial changes for cppcheck warnings

Merge series from Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>:

This can probably wait for the next merge window, I found a number of
cppcheck warnings that I didn't see in my last checks. The irony is
that the only really important issue found by cppcheck was on one of
my previous DPCM changes (submitted separately as a fix).