net: dsa: mv88e6xxx: Remove stale comment

GPIOF_DIR_* definitions are legacy and subject to remove.
Taking this into account, remove stale comment.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Link: https://patch.msgid.link/20240827171005.2301845-1-andriy.shevchenko@linux.intel.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>