swconfig: swlib.c: remove const qualifier for val.s since this is supposed to be free'd

Signed-off-by: Alexandru Ardelean <ardeleanalex@gmail.com>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@46230 3c298f89-4303-0410-b956-a3cf2f4a3e73