update_submodules: Add an empty log line between each iteration

For better readability of the log output, add an empty line between each
iteration of the submodules.

Change-Id: I626b609e9833bffde0f7a5eb101877c6cd83a173
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/87822
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>

util/scripts/update_submodules

@@ -96,6 +96,7 @@ main() {
 	fi
 
 	for submodule in "${submodule_dirs[@]}"; do
+		echo ""
 		echo "Checking submodule ${submodule}"
 		if ! cd "$submodule"; then
  			echo "Error: could not cd to $submodule"