serial: max310x: add comments for PLL limits Add comments to help clarify the provenance of the various hardcoded values used in computing the ref clk. Assisted-by: Gemini:Pro Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com> Link: https://patch.msgid.link/20260417-max310x-2-v1-10-b424e105ecac@dimonoff.com Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>