dosfstools: fix host variant dependencies

host-dosfstools shouldn't pull host-libiconv in since that's for
uClibc-based toolchains and we don't have that package anyway.
Fixes:
http://autobuild.buildroot.net/results/7637985bfb0afdd9217c297e9b0ac5de797c137d/



Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Acked-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>