v4l: Export v4l2-common.h in include/linux/Kbuild

v4l2-common.h is a header file that's used in user space, thus it must be
exported using header-y.
Signed-off-by: Sakari Ailus <sakari.ailus@iki.fi>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Tested-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

include/linux/Kbuild

@@ -382,6 +382,7 @@ header-y += usbdevice_fs.h
 header-y += utime.h
 header-y += utsname.h
 header-y += uvcvideo.h
+header-y += v4l2-common.h
 header-y += v4l2-dv-timings.h
 header-y += v4l2-mediabus.h
 header-y += v4l2-subdev.h