clk: meson: vid-pll-div: remove warning and return 0 on invalid config

The vid_pll_div is a programmable fractional divider, but vendor gives a
limited of known configuration value and it's corresponding fraction.

Thus when at reset value (0) or unknown value, we cannot determine the
result rate.

The initial behaviour was to print a warning, but the warning triggers
at each boot and when the clock tree is refreshed.

This patch moves the print to debug and returns 0 instead of the
parent rate.

Fixes: 72dbb8c9 ("clk: meson: Add vid_pll divider driver")
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Jerome Brunet <jbrunet@baylibre.com>
Link: https://lkml.kernel.org/r/20190327151348.27402-1-narmstrong@baylibre.com