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

drivers/gpu/drm/i915/display/intel_cdclk.c

@@ -1180,7 +1180,7 @@ static void skl_sanitize_cdclk(struct drm_i915_private *dev_priv)
 	/* force cdclk programming */
 	dev_priv->display.cdclk.hw.cdclk = 0;
 	/* force full PLL disable + enable */
-	dev_priv->display.cdclk.hw.vco = -1;
+	dev_priv->display.cdclk.hw.vco = ~0;
 }
 
 static void skl_cdclk_init_hw(struct drm_i915_private *dev_priv)
@@ -2075,7 +2075,7 @@ static void bxt_sanitize_cdclk(struct drm_i915_private *dev_priv)
 	dev_priv->display.cdclk.hw.cdclk = 0;
 
 	/* force full PLL disable + enable */
-	dev_priv->display.cdclk.hw.vco = -1;
+	dev_priv->display.cdclk.hw.vco = ~0;
 }
 
 static void bxt_cdclk_init_hw(struct drm_i915_private *dev_priv)