fastrpc: apps_user: check args before freeing.

args pointer can be uninitalized before calling free.
Code path for this is via VERIFYC macro jumping to bail label
which is not very explicit from the code.

Fixes: 7797ba9c (apps_user: fix memory leak)
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>