When lv-map and new-quant are enabled together,
av1_read_coeffs_txb currently does not use the new-quant
lookup table to get the dequantized value, which causes an
encode/decode mismatch. This patch fixes the function to
make lv-map work with new-quant.

Change-Id: I02a5521c3b412ae1c0b960cead7acd14a835c1fe