flite: fix <pkg>_LICENSE_FILES

Following commit dd4bcebd7c43212650cccc2494527dc3d69024d9 ("flite: use
FLITE_STRIP_COMPONENTS and FLITE_SUBDIR"), the FLITE_LICENSE_FILES was
no longer pointing to existing directories, which was breaking
legal-info.

Fixes:

  http://autobuild.buildroot.org/results/798/7983ec41a3f136bd997ebbfc110c7fc51ad79717/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/flite/flite.mk

@@ -25,7 +25,7 @@ FLITE_SITE = http://www.speech.cs.cmu.edu/flite/packed/flite-$(FLITE_VERSION)
 FLITE_STRIP_COMPONENTS = 0
 FLITE_SUBDIR = flite-$(FLITE_VERSION)-release
 FLITE_LICENSE = BSD-4c
-FLITE_LICENSE_FILES = COPYING
+FLITE_LICENSE_FILES = $(FLITE_SUBDIR)/COPYING
 
 FLITE_INSTALL_STAGING = YES
 # Patching configure.in