binutils: run install twice instead of overwriting the final toolchain with the initial one

fixes compiler error after a binutils rebuild/reinstall without
rebuilding the rest of the toolchain

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@43785 3c298f89-4303-0410-b956-a3cf2f4a3e73