If an error fatal to kmemleak (like memory allocation failure) happens,
kmemleak disables itself but it also removes the access to any
previously found memory leaks. This patch allows read-only access to the
kmemleak debugfs interface but disables any other action.
Reported-by: NNick Bowler <nbowler@elliptictech.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>