clk: imx: Fix fractional clock set rate computation

Before multiplying by PLL_FRAC_DENOM, the temp64 needs to be
 temp64 = rate * 2 - divfi * parent_rate * 8, instead of:
 temp64 = (rate * 2 - divfi) * parent_rate

Fixes: 6209624b

 ("clk: imx: Add fractional PLL output clock")
Signed-off-by: Abel Vesa <abel.vesa@nxp.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>