clk: sunxi-ng: a33: Add offset and minimum value for DDR1 PLL N factor

The DDR1 PLL on the A33 is an oddball amongst the A33 CCU clocks.
It is a clock multiplier, with the effective multiplier in the
range of 12 ~ 255 and no offset between the multiplier value and
the value programmed into the register.

Implement the zero offset and minimum value of 12 for this clock.

Fixes: d05c748b

 ("clk: sunxi-ng: Add A33 CCU support")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>