diag: Fix possible kernel addresses leak

This patch addresses kernel addresses leak by changing
the format specifier to adhere to the kptr_restrict system setting.

CRs-Fixed: 987013
Change-Id: I32649a26f54d96c56d80aa2a1bd5f5d9dd0dd9d3
Signed-off-by: Manoj Prabhu B <bmanoj@codeaurora.org>