msm: audio: qdsp6v2 Fix error handling in memory registration

Three instances of incorrect error path handling.  The first two
didn't initialize the 'result' variable before return (reported by Rob
Clark <rob.clark@linaro.org>).  The third was comparing the address of
a local variable against NULL, which will never be true.

Change-Id: Ia318c9331cc0ff896c4073389f3e666fa19eb4af
Signed-off-by: David Brown <davidb@codeaurora.org>