serial: max3100: Convert to_max3100_port() to be static inline

As Jiri rightfully pointed out the current to_max3100_port() macro
implementation is fragile in a sense that it expects the variable
name to be port, otherwise it blow up the build.

Change this to be static inline to prevent bad compilation.

Suggested-by: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Link: https://lore.kernel.org/r/20240410141135.1378948-1-andriy.shevchenko@linux.intel.com


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