bs1770gain uses wrong parameters

[pszxzsd]

Applying replaygain with bs1770gain uses the parameter -it which means get integrated loudness and calculate true peak.

Specifying -i is just superfluous because that's the default anyway and -t is wrong for two reasons:

1. Replaygain specifies sample peak, not any other fancy peak calculation methods
2. Calculating true peak is horrrrribly slow, the whole process is like 10x slower with this

Solution: invoke bs1770gain with parameter -p instead to calculate the correct peak gain and get a major speed boost as a bonus.

[sampsyo]

This does look like a bug! I don't know why those were chosen originally, but let's fix them.