tests/hbitmap: use ARRAY_SIZE macro

Applied using the Coccinelle semantic patch scripts/coccinelle/use_osdep.cocci

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>