uboot-tools: fix build failure for the target

The patch to drop config.h is still required, it just needed a tweak.
Fixes:
http://autobuild.buildroot.net/results/3653c0e3ec460c710524468987d5192337cf210e/



Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>