Patch from George G. Davis

As reported by various folks on the ARM Linux kernel mailing list,
the video-buf.ko driver has undefined references on all ARM machines
which use it as observed during `make modules`:

Warning: "v4wb_clear_user_page" [drivers/media/video/video-buf.ko] undefined!

Similar warnings exist for all ARM machines which use this driver.
So this change adds the missing EXPORT_SYMBOLs to allow using this
driver as a module.
Signed-off-by: NGeorge G. Davis <gdavis@mvista.com>
Signed-off-by: NRussell King <rmk+kernel@arm.linux.org.uk>