msm: adsprpc: Fix NULL pointer error when DEBUG_FS is disabled

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

Change-Id: I46ff3b8b27b53ff5bb5dead78ccdefc410435dda
Acked-by: Tadakamalla Krishnaiah <ktadakam@qti.qualcomm.com>
Signed-off-by: Mohammed Nayeem Ur Rahman <mohara@codeaurora.org>