diag: Check for valid proc id while querying real time status

Currently in diag driver invalid proc id may lead to accessing
invalid array elements. This patch fixes the issue.

Change-Id: I4bcf3eb610537c589d0b66903df1e79a88127b93
CRs-fixed: 629864
Signed-off-by: Katish Paran <kparan@codeaurora.org>