kernel/rv1106: SARADC VERIFIED — fixed -22 (vref-supply, not clk)

The saradc -22 was regulator_get_voltage on a dummy vref (no vref-supply in
DT), not the clk divider. Added vcc_1v8 fixed 1.8V regulator + vref-supply
(matching the vendor 86-panel). iio:device0 now reads both channels
(in_voltage0_raw=1023, in_voltage1_raw=246) — the adc-keys path works.

Five drivers verified this run: wifi, TRNG, OTP, GMAC, SARADC.
adc/SARADC-FIX.md; DRIVER-PARITY updated.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017wB8KB3MMQztRDXCMCkPrf

kernel/rv1106-enablement/adc/SARADC-FIX.md

@@ -0,0 +1,19 @@
+# SARADC — ✅ VERIFIED on warden-c8a3 (2026-08-25); the -22 was vref, not clk
+
+The rockchip_saradc probe failed `-22` NOT at clk_set_rate (no "failed to set
+adc clk rate" ever printed) but at `regulator_get_voltage(info->vref)` — with no
+`vref-supply` in DT the driver got a **dummy** regulator, and
+`regulator_get_voltage(dummy)` returns -EINVAL, which probe returns directly (so
+only the generic "probe failed with error -22" showed). The earlier
+clk-rv1106-divider theory was wrong (the divider is HIWORD settable, xin24m is
+registered; clk_set_rate would clamp, not fail).
+
+**Fix (DT only):** add the 1.8 V reference the vendor 86-panel uses —
+```dts
+/ { vcc_1v8: vcc-1v8 { compatible = "regulator-fixed"; regulator-name = "vcc_1v8";
+      regulator-always-on; regulator-boot-on;
+      regulator-min-microvolt = <1800000>; regulator-max-microvolt = <1800000>; }; };
+&saradc { vref-supply = <&vcc_1v8>; status = "okay"; };
+```
+**Evidence:** `iio:device0` (`ff3c0000.saradc`), `in_voltage0_raw=1023`,
+`in_voltage1_raw=246` — both channels read real analog values (the adc-keys path).