firmware: fix MMCM multiplier & divisor calculation
firmware: fix MMCM multiplier & divisor calculation

Also warn if the calculated VCO frequency strays outside the
datasheet specified range

Signed-off-by: Rohit Singh <6ceda7e05522ab1ffa85567e8d4e2bc048e6b44c@gmail.com>

mithro/HDMI2USB-litex-firmware,mithro/HDMI2USB-litex-firmware,mithro/HDMI2USB-litex-firmware,mithro/HDMI2USB-litex-firmware