base-files: fix sysupgrade 'wget' handling for uclient-fetch

base-files: fix sysupgrade 'wget' handling for uclient-fetch

change 48451 tried to add support for uclient-fetch by moving
/usr/bin/wget to /bin/wget, but this change kept the symbolic
link to /bin/busybox as install_bin creates links to param 1

the desired fix is to link to uclient-fetch to wget:
  install_bin /bin/uclient-fetch /bin/wget

Signed-off-by: John Clark <inindev@gmail.com>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@48483 3c298f89-4303-0410-b956-a3cf2f4a3e73