diag: Update diag get log request structure

Currently diag get log mask is using structure with
num_items which is not being used. The patch updates
structure for diag get log mask request.

Change-Id: I1d4d110ca1793e1c8bedcab33e2626f02af37926
Signed-off-by: Hardik Arya <harya@codeaurora.org>