scripts/bloat-o-meter: ignore changes in the size of linux_banner

linux_banner can change size due to changes in the compiler, build number,
or the user@host the system was compiled on; ignore size changes in
linux_banner entirely.

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Michal Marek <mmarek@suse.cz>