x86/tty/serial/8250: Resolve missing-field-initializers warnings

Resolve some missing-field-initializers warnings by using
designated initialization in the expansion of the
SERIAL_PORT_DFNS macro.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Link: http://lkml.kernel.org/r/1409972149-26272-1-git-send-email-jeffrey.t.kirsher@intel.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>