package/rtl8189es: fix build failure due to wrong endianness

At the moment rtl8189es module has -DCONFIG_LITTLE_ENDIAN hardcoded and
there is no way to override it. So to do this let's add a patch that is
pending upstream[1] to allow to override CFLAGS and then let's undefine
CONFIG_LITTLE_ENDIAN and define the correct endianness in rtl8189es.mk

Fixes:
http://autobuild.buildroot.net/results/3bcad5e88876c86a2a3338961ed20f28b5953779/

[1]: https://github.com/jwrdegoede/rtl8189ES_linux/pull/83



Signed-off-by: Giulio Benetti <giulio.benetti@benettiengineering.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>