arch: remove incorrect condition for endian definition on SuperH

Probably due to some copy/paste mistake, Config.in.sh was defining
BR2_ENDIAN to "LITTLE" when the architecture is BR2_x86_64. Due to the
fact that Config.in.sh is never included when we are building for
x86_64, this is a no-op, but is certainly good to clean up.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>