clk: sunxi-ng: Mask nkmp factors when setting register

Currently, if one of the factors isn't present, bit 0 gets always set to
1. For example, A83T has NMP PLLs modelled as NKMP PLL without K. Since
K is not specified, it's offset, width and shift is 0. Driver assumes
that lowest value possible is 1, otherwise we would get division by 0.
That situation causes that bit 0 is always set, which may change wanted
clock rate.

Fix that by masking every factor according to it's specified width.
Factors with width set to 0 won't have any influence to final register
value.

Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>