V4L/DVB (4430): Quickcam_messenger compilation fix

In bugzilla #6943, Maxim Britov reported:
"I can enable Logitech quickcam support in .config, but it want be compile.
I have to add into drivers/media/video/Makefile:
obj-$(CONFIG_USB_QUICKCAM_MESSENGER)    += usbvideo/"
He's right, just enable that driver as module while disabling every other
driver that gets into that directory, nothing will get compiled.
This patch fixes the Makefile.

Signed-off-by: Diego Calleja <diegocg@gmail.com>
Acked-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>