Makefile: rename non-user-facing variable

Variables should be prefixed with BR_ when they are not user-facing.

As a side effect, the new variable is prettier than the previous one. :-)

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
2 files changed