msm: adsprpc: Check validity of perf pointer

Check context perf pointer before dereferencing it.

Change-Id: I1c4a96361264e17691edba21a3f1e6bd23602e3b
Acked-by: Deepika Singh <dsi@qti.qualcomm.com>
Signed-off-by: Vamsi krishna Gattupalli <vgattupa@codeaurora.org>