rock-5-itx: link upstream kernel commit in pcie3 refclk u-boot patch (#9861)

Add a reference to Heiko's Linux mainline commit e684f02492f9 that
introduced the pcie30_port{0,1}_refclk gated-fixed-clock on this
board, so reviewers of the U-Boot dtsi override can see the
kernel-side rationale. Suggested by @rpardini on PR #9848.

Signed-off-by: SuperKali <hello@superkali.me>

Author: SuperKali

patch/u-boot/v2026.04/board_rock-5-itx/0001-arm-dts-rockchip-rock-5-itx-drop-pcie-refclk-from-u-boot-dtsi.patch

@@ -21,6 +21,10 @@ PI6C oscillator stays powered and the "ref" input ticks regardless of
 U-Boot's clock setup. The kernel keeps the full clocks list from its
 own DTB and is unaffected.
 
+See Linux mainline commit e684f02492f9 ("arm64: dts: rockchip: fix the
+pcie refclock oscillator on Rock 5 ITX") for the kernel-side rationale.
+
+Link: https://lore.kernel.org/r/20240906082511.2963890-6-heiko@sntech.de
 Signed-off-by: SuperKali <hello@superkali.me>
 ---
  arch/arm/dts/rk3588-rock-5-itx-u-boot.dtsi | 20 ++++++++++