media: ddbridge: shut up a new warning

drivers/media/pci/ddbridge/ddbridge-ci.c:321:5: warning: no previous prototype for 'ddb_ci_attach' [-Wmissing-prototypes]
 int ddb_ci_attach(struct ddb_port *port, u32 bitrate)
     ^~~~~~~~~~~~~

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>