audio/soundtouch: Switch to MASTER_SITES and fix i386

Switch to static tarball, unbreak i386 builds

References:
https://codeberg.org/soundtouch/soundtouch
https://lists.freebsd.org/archives/freebsd-pkg-fallout/2021-October/124516.html

PR: 259173
Approved by: crees (port maintainer), arrowd (mentor)
Differential Revision: https://reviews.freebsd.org/D32639