busybox: Add missing INITSCRIPT_NAME_${PN}-hwclock

busybox: Add missing INITSCRIPT_NAME_${PN}-hwclock

Fix failures like:

Configuring busybox-hwclock.
usage: update-rc.d [-n] [-f] [-r <root>] <basename> remove
       update-rc.d [-n] [-r <root>] [-s] <basename> defaults [NN | sNN kNN]
       update-rc.d [-n] [-r <root>] [-s] <basename> start|stop NN runlvl [runlvl] [...] .
                -n: not really
                -f: force
                -v: verbose
                -r: alternate root path (default is /)
                -s: invoke start methods if appropriate to current runlevel
Collected errors:
 * pkg_run_script: package "busybox-hwclock" postinst script returned status 1.
 * opkg_configure: busybox-hwclock.postinst returned 1.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>