cogl: correcting the cogl trace log

Remove the extra & symbol appearing in cogl debug log

!1517
8 jobs for !1517 with cogl-log-correction in 11 minutes and 9 seconds
detached
Status Job ID Name Coverage
  Review
passed #949475
check-commit-log

00:00:30

 
  Build
passed #949476
build-mutter

00:03:43

passed #949478
build-without-native-backend-and-wayland

00:03:02

passed #949477
build-without-opengl-and-glx

00:03:14

 
  Test
passed #949480
can-build-gnome-shell

00:01:43

passed #949524
test-mutter

00:05:43

failed #949504
test-mutter

00:06:05

failed #949479
test-mutter

00:05:15