diag: Sanitize the proc values against NUM_DIAG_MD_DEV

Sanitize the proc values against the maximum number of procs
to prevent possible out of bound issues and initialize the buffer
to prevent accessing uninitialized one.

Change-Id: I3ff65a6c6bab0a7d3967782269058ec017644ac8
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>