serial: imx: stop casting struct uart_port to struct imx_port

serial: imx: stop casting struct uart_port to struct imx_port

struct imx_port does have a struct uart_port as its first member, so
the current code works, but it is not how kernel code is usually
written.

Similar to many other serial drivers, introduce and use a
to_imx_port() helper based on container_of(). No functional change.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Link: https://lore.kernel.org/r/20240528094022.2161066-1-linux@rasmusvillemoes.dk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>