Comment # 2 on bug 1210163 from Fabian Vogt

> Kernel Panic - not syncing: VFS: Unable to mount root fs on unknown-block(8,5)

This is actually about mounting the initramfs. I suspect it's simply corrupt or
for some reason not loaded correctly.

I suggest you run "dracut -f" when booting with the working kernel+initrd and
try again.