http://daemonizer.de/prism54/prism54-fw/fw-usb/2.13.1.0.arm.0 is 404 for a long time now. http://daemonizer.de/prism54/prism54-fw/fw-usb/2.13.1.0.lm86.arm is apparently the correct link (it's the same file). Please fix the ebuild (SRC_URI and newins ... isl3886usb), otherwise emerge fails.
See, e.g. http://kernel.ubuntu.com/git?p=ubuntu-archive/linux-firmware-karmic.git;a=commitdiff;h=389a94556ea44f193bdc87460d2df93d60fda191
Hi, is this ebuild maintained at all? This is a simple fix. Granted, the version is unstable, but it should probably have been stabilized long time ago (stable version is for old kernels).
Problem fixed. For marking it stable later feel free to open a new bug.