x264enc: Don't set max latency to the same value as the encoder latency

x264enc: Don't set max latency to the same value as the encoder latency

The meaning of the max latency is *not* the maximum latency this element will
introduce. It is the maximum latency this element can endure without
overflowing any buffers, which is infinite for x264enc.

Fixes latency configuration in zero latency mode, where max latency was
becoming 0... which usually won't work well if something else introduces
latency as then max < min in the end, and latency configuration just fails.