Correctly initialize "ones" value in neon quantize

By using 0xff for a short it was not setting the high bits. When
comparing the output with vtst to find non-zero elements it was skipping
vaules which had no low bits set such as -512 / 0xFE00.

Using -8191 as the first element of coeff will generate this condition.

BUG=883

Change-Id: Ia1e10fb809d1e7866f28c56769fe703e6231a657