Documentation: serial: link uart_ops properly

The syntax to reference a struct in text is "struct XY". So reference
uart_ops properly, so that hyperlinks work.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20220728061056.20799-4-jslaby@suse.cz


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