clk: sunxi-ng: mult: Fix minimum in round rate

The previous code was always taking 1 as the minimum in it's round_rate
function, ignoring entirely what was set as minimum in the clock
definition.

Make sure that's not the case anymore.

Fixes: 2beaa601 ("clk: sunxi-ng: Implement minimum for multipliers")
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>