scripts/dtc: Fix a resource leak

scripts/dtc: Fix a resource leak

during a check of the current git head of the linux kernel with the
static code analysis tool cppcheck
(http://sourceforge.net/apps/mediawiki/cppcheck/index.php?title=Main_Page)
the tool discovered a resource leak in linux-2.6/scripts/dtc/fstree.c.

Please refer the attached patch, that fixes the issue.

Fixes https://bugzilla.kernel.org/show_bug.cgi?id=15363
Signed-off-by: Martin Ettl <ettl.martin@gmx.de>
Cc: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Michal Marek <mmarek@suse.cz>