V4L/DVB (5156): Fix: dma free is being called with wrong arguments

Functions buffer_release() in bttv-driver.c and
vbi_buffer_release() in bttv-vbi.c are ending with:
      bttv_dma_free(&fh->cap,fh->btv,buf);

For vbi it seems to be wrong. Both functions should end with:

      bttv_dma_free(q,fh->btv,buf);
Thanks to Peter Schlaf <peter.schlaf@web.de> for pointing this.

Signed-off-by: Michael H. Schimek <mschimek@gmx.at>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>