imx: mx7ulp: Fix SPLL/APLL clock rate calculation issue

The num/denom is a float value, but in the calculation it is convert
to integer 0, and wrong result.

Signed-off-by: Ye Li <ye.li@nxp.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>