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 Job ID Name Coverage
  Preparation
passed #81737
gst indent

00:00:33

passed #81736
manifest

00:00:20

 
  Build
passed #81738
build fedora x86_64

00:03:14

 
  Test
passed #81739
check fedora

00:03:30

 
  Full Builds
passed #81740
build android arm64 api28

00:05:01

passed #81742
build cerbero cross win32

00:06:56

passed #81743
build cerbero cross win64

00:10:37

passed #81741
build cerbero fedora x86_64

00:07:44