libbsd: correct license file reference

Fixes autobuilder error:
http://autobuild.buildroot.net/results/ccd/ccd2f3fe69a3e0321685daf95f85eca5ba2d64cf/

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

package/libbsd/libbsd.mk

@@ -8,7 +8,7 @@ LIBBSD_VERSION         = 0.4.2
 LIBBSD_SOURCE          = libbsd-$(LIBBSD_VERSION).tar.gz
 LIBBSD_SITE            = http://libbsd.freedesktop.org/releases
 LIBBSD_LICENSE         = BSD-3c MIT
-LIBBSD_LICENSE_FILES   = LICENSE
+LIBBSD_LICENSE_FILES   = COPYING
 
 # man-pages are BSD-4c, so that license only matters
 # if doc is kept in the target rootfs