Kmemleak should only track valid scan areas with a non-zero size.
Otherwise, such area may reside just at the end of an object and
kmemleak would report "Adding scan area to unknown object".
Signed-off-by: NTiejun Chen <tiejun.chen@windriver.com>
Signed-off-by: NCatalin Marinas <catalin.marinas@arm.com>