SERIAL: MIPS Swarm sb1250-duart.c driver needs module.h

This driver is a module and needs module.h, otherwise it will break when
we remove a bogus usage of module.h from one of the other MIPS headers.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/3447/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>