Could the maintainer please rebuild the package?
The package linux-source-4.19.20-next-sunxi has the kernel source code in a tarball linux-source-4.19.20-sunxi.tar.xz, but that tarball has an error in it.
It contains the following link:
wireguard -> /home/igorp/samsung/cache/sources/wireguard/src
This is an oops on Igor's part.
Incidentally, I found a number of broken links, I'm not sure if these are all errors:
/usr/src$ find -follow -type l -ls
142207 0 lrwxrwxrwx 1 root root 47 Feb 9 11:01 ./net/wireguard -> /home/igorp/samsung/cache/sources/wireguard/src
634352 0 lrwxrwxrwx 1 root root 28 Dec 27 00:53 ./debian/hdrtmp/usr/src/linux-headers-4.19.20-sunxi/scripts/dtc/include-prefixes/nios2 -> ../../../arch/nios2/boot/dts
634353 0 lrwxrwxrwx 1 root root 30 Dec 27 00:53 ./debian/hdrtmp/usr/src/linux-headers-4.19.20-sunxi/scripts/dtc/include-prefixes/powerpc -> ../../../arch/powerpc/boot/dts
269401 0 lrwxrwxrwx 1 root root 36 Feb 9 10:41 ./debian/hdrtmp/lib/modules/4.19.20-sunxi/build -> /usr/src/linux-headers-4.19.20-sunxi
616013 0 lrwxrwxrwx 1 root root 48 Feb 9 11:01 ./drivers/net/wireless/rtl8812au/core -> /home/igorp/samsung/cache/sources/rtl8812au/core
616009 0 lrwxrwxrwx 1 root root 57 Feb 9 11:01 ./drivers/net/wireless/rtl8812au/modules.order -> /home/igorp/samsung/cache/sources/rtl8812au/modules.order
616016 0 lrwxrwxrwx 1 root root 50 Feb 9 11:01 ./drivers/net/wireless/rtl8812au/os_dep -> /home/igorp/samsung/cache/sources/rtl8812au/os_dep
616015 0 lrwxrwxrwx 1 root root 47 Feb 9 11:01 ./drivers/net/wireless/rtl8812au/hal -> /home/igorp/samsung/cache/sources/rtl8812au/hal
616011 0 lrwxrwxrwx 1 root root 51 Feb 9 11:01 ./drivers/net/wireless/rtl8812au/include -> /home/igorp/samsung/cache/sources/rtl8812au/include
616010 0 lrwxrwxrwx 1 root root 52 Feb 9 11:01 ./drivers/net/wireless/rtl8812au/platform -> /home/igorp/samsung/cache/sources/rtl8812au/platform