clk: sunxi-ng: select SUNXI_CCU_MULT for sun5i

We get a link error when CCU_MULT is not set with the
newly added driver:

drivers/clk/sunxi-ng/ccu-sun5i.o:(.data.__compound_literal.17+0x4): undefined reference to `ccu_mult_ops'
drivers/clk/sunxi-ng/ccu-sun5i.o:(.data.__compound_literal.5+0x4): undefined reference to `ccu_mult_ops'

Fixes: 5e737617 ("clk: sunxi-ng: Add sun5i CCU driver")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>