diag: Add kmemleak_not_leak check to avoid memleak

Add kmemleak_not_leak check in diagchar initialization to
avoid memleaks since this is not a leak case.

Change-Id: I72e208ec88f75d549458508e9f83d6af07c49a78
Signed-off-by: Katish Paran <kparan@codeaurora.org>