swconfig: libsw.so should be installed into /usr/lib/

otherwise it's not picked up by toolchain:

staging_dir/toolchain-mipsel_24kec+dsp_gcc-4.8-linaro_musl-1.1.10/lib/gcc/mipsel-openwrt-linux-musl/4.8.3/../../../../mipsel-openwrt-linux-musl/bin/ld: cannot find -lsw

Signed-off-by: Roman Yeryomin <roman@advem.lv>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@46406 3c298f89-4303-0410-b956-a3cf2f4a3e73