serial: max310x: add comments for membase address workaround

Add comments about workaround used to configure membase address. This
follows suggestions made during review of a sc16is7xx driver patch to
add the same workaround.

Link: https://lore.kernel.org/lkml/2936e18f-44ea-faed-9fa0-2ddefe7c3194@linux.intel.com
Link: https://lore.kernel.org/lkml/20230801131655.80bd8f97f018dda6155d65f6@hugovil.com/


Signed-off-by: Hugo Villeneuve <hvilleneuve@dimonoff.com>
Link: https://lore.kernel.org/r/20230803140551.970141-1-hugo@hugovil.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>