Makefile: drop -D__CHECK_ENDIAN__ from cflags

That's the default now, no need for makefiles to set it.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Kalle Valo <kvalo@codeaurora.org>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Acked-by: Marc Kleine-Budde <mkl@pengutronix.de>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Arend van Spriel <arend.vanspriel@broadcom.com>