vortex_wtdma_bufshift() function does calculate the page index
wrongly, first masking then shift, which always results in zero.
The proper computation is to first shift, then mask.
Reported-by: NDan Carpenter <dan.carpenter@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>