diag: Add checks in initialization functions

Diag driver has a set of services to initialize during driver
initialization. These initializations can fail leading to
incoherent state. Add checks to make sure that all the
services are initialized properly.

Change-Id: I831254894a69d1be1d388a6cc587a7f3bfc838d3
CRs-Fixed: 610301
Signed-off-by: Ravi Aravamudhan <aravamud@codeaurora.org>