scripts: headers_install: Turn CONFIG_* leak checker to report error

By default CONFIG_* user-space leak checker marks it as warning but
we should mark them as error so that we can catch such usage at the
compile time itself.

Change-Id: I5f14f7f881e46843f2e0cc0957fc0b730e76aa93
Signed-off-by: Trilok Soni <tsoni@codeaurora.org>