checkpatch: Fix Python style violation.

I introduced this when updating the script before commit.  My fault, sorry.

Fixes: c599d5ccf3 (checkpatch.py: A simple script for finding patch issues)
Signed-off-by: Ben Pfaff <blp@ovn.org>

utilities/checkpatch.py

@@ -185,6 +185,7 @@ def usage():
     print("-t|--skip-trailing-whitespace\t"
           "Skips the trailing whitespace test")
 
+
 def ovs_checkpatch_file(filename):
     try:
         mail = email.message_from_file(open(filename, 'r'))