dma-direct: don't call dma_set_decrypted for remapped allocations

Remapped allocations handle the encrypted bit through the pgprot passed
to vmap, so there is no call dma_set_decrypted.  Note that this case is
currently entirely theoretical as no valid kernel configuration supports
remapped allocations and memory encryption currently.

Signed-off-by: Christoph Hellwig <hch@lst.de>