compile_pkgs: try to fix problem with symlinks

This should consistently expand path to compile_pkgs script no matter if
symbolic link for used or not.

compile_pkgs

@@ -28,8 +28,8 @@ _die() {
 }
 
 # Paths to OpenWRT build and turris-build sources
-src_dir="$(readlink -f "$(dirname "$0")")"
-build_dir="$(pwd)"
+src_dir="$(dirname "$(readlink -f "$0")")"
+build_dir="$(readlink -f "$(pwd)")"
 if [ "$build_dir" == "$src_dir" ]; then
 	# Protect against turris-build repository wipe
 	mkdir -p build