V4L/DVB (3527): VIDEO_CPIA2 must depend on USB

V4L/DVB (3527): VIDEO_CPIA2 must depend on USB

CONFIG_VIDEO_CPIA2=y, CONFIG_USB=n results in the following compile
<--  snip  -->
...
  LD      .tmp_vmlinux1
drivers/built-in.o: In function `set_alternate':cpia2_usb.c:(.text+0x443aa2): undefined reference to `usb_set_interface'
drivers/built-in.o: In function `cpia2_usb_stream_resume': undefined reference to `usb_alloc_urb'
drivers/built-in.o: In function `cpia2_usb_stream_resume': undefined reference to `usb_submit_urb'
drivers/built-in.o: In function `cpia2_usb_stream_pause': undefined reference to `usb_kill_urb'
drivers/built-in.o: In function `cpia2_usb_stream_pause': undefined reference to `usb_free_urb'
drivers/built-in.o: In function `cpia2_usb_disconnect':cpia2_usb.c:(.text+0x443e14): undefined reference to `usb_driver_release_interface'
drivers/built-in.o: In function `cpia2_usb_transfer_cmd': undefined reference to `usb_control_msg'
drivers/built-in.o: In function `cpia2_usb_transfer_cmd': undefined reference to `usb_control_msg'
drivers/built-in.o: In function `cpia2_usb_complete':cpia2_usb.c:(.text+0x444836): undefined reference to `usb_submit_urb'
drivers/built-in.o: In function `cpia2_usb_cleanup': undefined reference to `usb_deregister'
drivers/built-in.o: In function `cpia2_usb_init': undefined reference to `usb_register_driver'

Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>