[media] b2c2: export b2c2_flexcop_debug symbol

ERROR: "b2c2_flexcop_debug" [drivers/media/pci/b2c2/b2c2-flexcop-pci.ko] undefined!

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>