flatcc: fix debug build

flatcc is named flatcc_d if BR2_ENABLE_DEBUG is set because of the
following line in CMakeLists.txt: set(CMAKE_DEBUG_POSTFIX "_d")

So update FLATCC_TARGET_REMOVE_FLATCC_COMPILER hook to replace flatcc
by flatcc*

Fixes:
 - http://autobuild.buildroot.org/results/a47f49cd2fdd809257bd7e83dca620f2e6aac85b



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>