[package] busybox: fix bad variable substitution on right hand side of I/O...

[package] busybox: fix bad variable substitution on right hand side of I/O redirection, imported patch from upstream bug 5282

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@32162 3c298f89-4303-0410-b956-a3cf2f4a3e73