drm/nouveau/disp/gt215: Fix HDA ELD handling (thus, HDMI audio) on gt215

Store the ELD correctly, not just enough copies of the first byte
to pad out the given ELD size.

Signed-off-by: Alastair Bridgewater <alastair.bridgewater@gmail.com>
Fixes: 120b0c39 ("drm/nv50-/disp: audit and version SOR_HDA_ELD method")
Cc: stable@vger.kernel.org # v3.17+
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>