drm/vmwgfx: Fix setting of dma masks

commit 4cbfa1e6c09e98450aab3240e5119b0ab2c9795b upstream.

Previously we set only the dma mask and not the coherent mask. Fix that.
Also, for clarity, make sure both are initially set to 64 bits.

Cc: <stable@vger.kernel.org>
Fixes: 0d00c488: ("drm/vmwgfx: Fix the driver for large dma addresses")
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Deepak Rawat <drawat@vmware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>