common: Rename macro appropriately

While doing code-review internally this got nitpicked by 2 reviewers, so
I decided to include this here.

Signed-off-by: Steffen Jaeckel <jaeckel-floss@eyet-services.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heiko Schocher <hs@denx.de>