kbuild: fix adjust_autoksyms.sh for modules that need only one symbol

When only one symbol was listed and therefore the line didn't contain
any space to separate multiple symbols, that symbol got ignored.
Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Michal Marek <mmarek@suse.com>

scripts/adjust_autoksyms.sh

@@ -59,7 +59,7 @@ cat > "$new_ksyms_file" << EOT
  */
 
 EOT
-sed -ns -e '3s/ /\n/gp' "$MODVERDIR"/*.mod | sort -u |
+sed -ns -e '3{s/ /\n/g;/^$/!p;}' "$MODVERDIR"/*.mod | sort -u |
 while read sym; do
 	if [ -n "$CONFIG_HAVE_UNDERSCORE_SYMBOL_PREFIX" ]; then
 		sym="${sym#_}"