msm:vidc: Fix NULL pointer when DEBUG_FS is gone

Add extra checks to avoid NULL pointer derefernce when DEBUG_FS
is disabled.

Change-Id: Ib4f1247828c2b4a01f2098e5a97b522c88fe658e
Signed-off-by: Jean Xiao <jianxiao@codeaurora.org>
Signed-off-by: Pranav Vashi <neobuddy89@gmail.com>