clk: sunxi-ng: select SUNXI_CCU_MULT for sun8i-a83t

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

drivers/clk/sunxi-ng/ccu-sun8i-a83t.o:(.data.__compound_literal.1+0x4): undefined reference to `ccu_mult_ops'
drivers/clk/sunxi-ng/ccu-sun8i-a83t.o:(.data.__compound_literal.3+0x4): undefined reference to `ccu_mult_ops'

Fixes: 46b492116666 ("clk: sunxi-ng: Add driver for A83T CCU")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Chen-Yu Tsai <wens@csie.org>