drm/i915/cdclk: s/-1/~0/ when dealing with unsigned values

cdclk_pll_is_unknown() used ~0 when checking for the "VCO is
unknown" value, but the assignment uses -1. They are the same
in the end, but let's use the same ~0 form on both sides for
consistency.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231128115138.13238-2-ville.syrjala@linux.intel.com


Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>