pad: Fix printf format when printing hook id

It's a gulong so we have to cast it to a guint64 when using it with
G_GUINT64_FORMAT.

Spotted by Vincent Penvern.
8 jobs for hook-id-printf-format in 19 minutes and 1 second (queued for 2 seconds)
Status Name Job ID Coverage
  Preparation
passed gst indent #81737

00:00:33

passed manifest #81736

00:00:20

 
  Build
passed build fedora x86_64 #81738

00:03:14

 
  Test
passed check fedora #81739

00:03:30

 
  Full Builds
passed build android arm64 api28 #81740

00:05:01

passed build cerbero cross win32 #81742

00:06:56

passed build cerbero cross win64 #81743

00:10:37

passed build cerbero fedora x86_64 #81741

00:07:44