lint: convert checkpatch_json.py to python 3

Align all coreboot scripts on one python version.

Tested by running the original suggested test:
 $ nice -n 20 git diff HEAD~ | util/lint/checkpatch.pl \
     --no-signoff -q - | tee checkpatch.txt
 $ util/lint/checkpatch_json.py checkpatch.txt \
     comment.json checkpatch.txt

Change-Id: Iec2bb0be23b27a3eaf92f293c962a8e6bfb03af0
Signed-off-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/42318
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by:  Felix Singer <felixsinger@posteo.net>

util/lint/checkpatch_json.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python2
+#!/usr/bin/env python3
 # SPDX-License-Identifier: GPL-2.0-only
 
 """
@@ -41,14 +41,14 @@ def parse_file(input_file):
 
 def main():
     if (len(sys.argv) < 3) or (sys.argv[1] == "-h"):
-        print "HELP:"
-        print  sys.argv[0] + " <input file> <output file in json>"
+        print("HELP:")
+        print(sys.argv[0] + " <input file> <output file in json>")
         sys.exit()
 
-    print sys.argv[1]
+    print(sys.argv[1])
     parse_file(sys.argv[1])
     data['comments'] = list_temp
-    print json.dumps(data)
+    print(json.dumps(data))
     out_file = open( sys.argv[2] , "w")
     json.dump(data, out_file, sort_keys=True, indent=4)
     out_file.close()